V2 PPP. KKPOirr OF-' ITvOdKKSS. C. E. BEECIIKU. 



rocks of the Chemung group in Pennsylvania. It somewhat 

 resembles J^J. ptistulosd, Whit I"., hut has more nodes and 

 ridges ornameuting the carapace, and is without t;he entirely 

 pustnlose surface of that species. ^. sithleois, ^yhitf.. has 

 hut 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 

 dilierent positions of the abdomen in relation to the cara- 

 pace, which have been observed, and illustrates the great 

 flexibility of this portion of the animal. Pig. 1 repre- 

 sents the abdomen extending in the direction of the longer 

 axis of the carapace, and probably shows the normal posi- 

 tion of the parts. In Fig. 2 the abdomen is elevated above 

 the dorsum. Fig. 3 shows the valves open, with the ab- 

 domen closeh^ curved around the posterior end of the left 

 valve. The specimen represented in Fig. 4 has- the posi- 

 tion 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 rep- 

 resented 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 re- 

 mains of fifteen separate individuals, nine of wiiich are 

 shown on the side represented in the figure. 



The specimens of Elymocaris s Hi qua, and Tropidocaris 

 hicariiiata. 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 crusta- 

 ceans are numerous species of lamellibranchiata in the same 

 occurrence ; also one or two species of brachiopoda, an Or- 

 thoceras 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 



