Page:Second Geological Survey of Pennsylvania Report of Progress PPP.djvu/26

 rocks of the Chemung group in Pennsylvania. It somewhat resembles E. pustulosa, Whitf., but has more nodes and ridges ornamenting the carapace, and is without the entirely pustulose surface of that species. E. sublevis, Whitf., has but a single row of spines on each abdominal somite, and the lateral ones are of considerable length.

The series represented in Figs. 1–4 of Plate I, shows the different positions of the abdomen in relation to the carapace, which have been observed, and illustrates the great flexibility of this portion of the animal. Fig. 1 represents the abdomen extending in the direction of the longer axis of the carapace, and probably shows the normal position of the parts. In Fig. 2 the abdomen is elevated above the dorsum. Fig. 3 shows the valves open, with the abdomen closely curved around the posterior end of the left valve. The specimen represented in Fig. 4 has the position of the abdomen the reverse of Fig. 1, extending obliquely from between the anterior ends of the valves. Specimens in the first and second of these positions are represented on the piece of rock shown in Fig. 12, which also illustrates the abundance of specimens in some portions of the shales. The single fragment in question contains the remains of fifteen separate individuals, nine of which are shown on the side represented in the figure.

The specimens of Elymocaris siliqua, and Tropidocaris bicarinata, which have been thus far found, are associated with this species.

Besides the remains of the crustaceans here described, there are also several fragments in the collections from these shales which belong to other forms of crustacea, but are too obscure to furnish satisfactory information as to their nature and characters. In addition to the crustaceans are numerous species of lamellibranchiata in the same occurrence; also one or two species of brachiopoda, an Orthoceras and the teeth and scales of fish.

The data furnished by the specimens of E. punctata and E. socialis fix the number of naked abdominal segments in the genus at six.

Formation and locality.—In the shales at the base of the