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separated from the colony, it is evident that we have a condition of life in this instance very different from that usually met with among lower animals, especially among the jelly-fishes. Apolemia is, without question, a colony composed of many members, which in younger stages are attached together in the form of a Siphonophore, but as it grows older, each colony breaks up into many fragments, each of which lives wholly independent of its neighbor. The growth of a fragment after it has been separated from its connections, has never been traced, and it is not known how long or short that life may be, but in other genera belonging to a group of Siphonophores, quite unlike the Physophoridæ, the whole history of the growth of such a fragment has been followed. Apolemia is very interesting from its relationship to this form known as Diphyes, the type of a large family of Siphonophores called the Diphyidæ. The anatomy of this animal will be pointed out in a paper to follow the present, after which its curious relatives can be better understood, and the reasons why they are not placed in the group with Agalma better appreciated.
THE LOESS IN CENTRAL IOIVA.
BY R. ELLSWORTH CALL.
the 16th of May last, the writer discovered unmistakable
loess under and around the city of Des Moines. Following are the details of the discovery, and such notes thereon as may be of general interest.
It might be well to remark that this formation has hitherta been known only in Western and Southwestern Iowa, as has been reported by the various surveys and explorations sustained by the General and State Governments; and in Southeastern Iowa, as reported on to the Muscatine Academy of Science, by Professor F. M. Witter, formerly of that city. He found the loess under certain portions of Muscatine, with its characteristic fossils, a list of which, if my memory serves me, he reported with his paper. A reference is made (White's Geology of Iowa, Vol. I, p. 114, foot note) to a deposit of the loess near the source of one of the branches of the Raccoon, east of the great water-shed of the State, but which of the three branches of the Raccoon is meant, or the locality of the deposit, is not indicated.
The occurrence of the loess in extensive outcrops, over areas subjected at a previous time to geological investigation, but of which no mention is made, and that, too, in Central Iowa, was wholly unexpected. The formation was first seen, and its true nature surmised, at a point some two and one-half miles west of the city of Des Moines, on a branch cut of the C. R. I. & P. R. R. The cutting was made in the course of building a branch to the State Fair Grounds, in the summer of 1880, but the nature and true geological age of the material through which it passed seems to have remained wholly unknown. Subsequently outcrops were seen and studied at various places in and around the city, and specimens of the soil, the characteristic concretions and fossils, were taken from them all. Some of these exposures, owing to recent excavations like those in process of completion on Capitol Hill, in East Des Moines, show the deposit to be very extensive, and indicate that the higher lands, for some distance to the east and west of the Des Moines river in this locality, are composed in great part of true loess.
Fig. I is representative of an actual section, as it may be seen at a point some three and one half miles above the city of Des Moines, on the river of that name. It will be seen from this section that the loess forms the bluff or face of the third terrace, and probably forms the mass of the higher land in the immediate vicinity of the stream. Beneath the loess is found the drift, and beneath that again the clays of the coal measures. The river has cut its channel, by corrasion, through the formations mentioned, and in some localities has eroded a channel through the sandstones found beneath the clays. Geologists will be able to form their own conclusions from these data, and see in them, perhaps, some of the
4 Fig. 1.-Section across Des Moines river, above the city of Des Moines, Iowa. 1, Terrace; 2, loess; 3, drist; 4, clay.
results of those great continental oscillations which have contributed so wonderfully to change the physical aspects of this region. The number and height of the terraces indicate extensive areas of depression and subsequent elevation.
It might here be noted that the lithological or physical features of these local deposits differ in no appreciable degree from the loess of the Missouri valley, with which it is probably synchronous, and also of the same ultimate origin. The fossils found in the loess at this point thus far, are a single spine of a fish, among the vertebrates, and among the invertebrates the following land and fresh-water shells : Mesodon thyroides Say, Patula alternata Say, P. striatella Anth., Hyalina arborea Say, Vallonia pulchella Müller, Stenotrema monodon Rack., Helicodiscus lineatus Say, Strobila labyrinthica Say, Pupa fallax Say, P. armifera Say, P. pentadon Say, Helicina oculata Say, Succinea obliqua Sar., Limnophysa humilis Say, and Limnophysa desidiosa (?) Say. Another species of the subgenus Patula, is, perhaps, P. strigosa Gould, and is represented by four specimens not well preserved. Root marks abound in some parts of the exposures. The woody matter having decayed, has left the cavity partially filled with carbonaceous material, while the mass of the concretion-like remains thus referred to vegetable origin, is strongly impregnated with the sesquioxide of iron. The presence of this oxide is in itself one of the strong reasons for regarding these remains as fragments of fossilized roots. It is not here necessary to revert to the composition of roots, for the reason that the fact of their containing a large per cent. of oxide of iron is well known. It has been thought best to record simply the finding of the loess in this vicinity, and leave to others the forming of any theories of the deposit.
NOTES ON THE EARLY LARVAL STAGES OF THE
FIDDLER CRAB, AND OF ALPHEUS.
BY A. S. PACKARD, JR. The Zoëa of Gelasimus pugnax.-While at Fort Macon, North Carolina, in 1870, I collected a number of the common fiddler crab (Gelasimus pugnax Smith) with eggs. May 15th segmentation had in some just taken place, the blastoderm having formed, while in others the zoëæ were about ready to hatch, and were seen to be surrounded in the eggs by a delicate larval membrane.
For want of time the crabs bearing the eggs were placed in alcohol and studied after my return to Salem. Hoping to get another opportunity to study the living embryos and larvæ, after waiting about ten years expecting that some of our carcinologists might describe the transformations of this interesting crab, I have decided to offer the following slight contribution to the subject, with the hope that a complete history of the development of the fiddler crab may yet be worked out.
Several eggs were observed in which one, two, or sometimes three large nucleated and nucleolated (blastodermic) cells (Fig. I, A) were observed lying on the periphery of the egg; they were more or less flattened, and the yolk on which they rested was hollowed out under them. When the chorion is ruptured they pass out whole as large round cells(d). Their large size seems unusual for polar blastodermic cells. They all appear to be, however, waste segmentation cells. In eggs farther advanced, and after the blastoderm has appeared, the yolk is seen to be surrounded by a distinct membrane.
In the next stages observed (B), the zoëa, with its appendages and large, dark, sessile eyes was formed. (C, the same freed from the egg shell or chorion.)
Upon rupturing the egg-membrane of the alcoholic specimens, I was enabled to work out the form of the larva just before hatching. The cephalothorax is large and spherical, not segmented, while the abdomen is long and slender, and composed of six definite somites; the last one ending in a forked tail, the rounded lobes provided each with three long setæ or bristles (D). I could detect no frontal or dorsal spine, though they were probably present in a rudimentary form. The antennæ are as represented at Fig. 1, I, II; the upper antenna (1) is conical, short and thick, without any terminal seta ; while the second or lower antenna (II) is much slenderer, rather longer, and ends in four very unequal setæ, the second seta from above being very much the larger. The mandibles are simple, and I could detect no palpus. The first maxilla (iv) is two lobed, the lobes representing two endopodites; the upper (palpus) is about half as thick as the lower, and the seta hair-like; those of the first (lower) endopodite are spine-like. Of the second maxilla (v) only the three inner lobes or endopodites were observed, the exopodites or what corresponds to the gill and scraper of the adult crab, unfortunately not having been worked out. The two maxillipeds (VI, VII) repeat each other in form; the basal joint giving rise to a simple d
Fig. 1.-A-D, young of Fiddler Crab; E, abdominal leg of larval Alpheus. exopodite (ex) and a four-jointed endopodite (en) in the first maxilliped, and a five-jointed one in the second. The new joints of the zoëa of the second stage and the first larval skin are to be seen in the figure.
Our knowledge of the zoëa forms of the crabs, or Brachyurous Decapoda is really quite limited, especially when we consider the first larval stage. Careful studies on the embryonic zoëa-forms only comprise those of Professor S. I. Smith and Mr. W. Faxon on the early stages of Hippa, those of Faxon and Professor Brooks on the early stages of Porcellana, and those of Faxon on the early stages of Carcinus menas and Panopeus sayi. Now the zoëa of Porcellana, Hippa and Pagurus are, in the abdominal and other characters, quite different from those of the higher crabs, and approach those of the shrimps and other Anomura, and this is what we might expect, as these forms are intermediate between the shrimps and true crabs. It is a matter of considerable interest to learn something of the zoëa of Gelasimus, as with Ocypoda it stands at the head of the crabs, above Cancer, Carcinus, Pano