ELYMOCARIS. PPP. 13 



Chemung group as exposed at Warren, Pa. ; belonging to 

 the upper strata of the series when considered in relation to 

 the entire thickness of the group in New York and Penn- 

 sylvania. 



ELYMOCARIS, Nov. gen. 

 ['5/y,u«-, siliqua; ^a/>:c, caris.'\ 



Carapace bivalve, dorsal line nearly equaling the length 

 of the valves. Valves elongate, longitudinally sub-quad- 

 rangular or sledge-shaped, extending posteriorly slightly 

 beyond the hinge-line. Margins thickened, regularly curv- 

 ing from the anterior extremity of the hinge, making a 

 broad sweep along the lower margin, rapidly curving around 

 the lower posterior end, and extending to the hinge. 



Cephalic region marked by a distinct optic node near the 

 anterior end of the valve, behind which are two low, broad 

 elevations. Thoracic portion regularly convex. Rostrum 

 unknown. 



Abdomen composed of two naked segments. Telson con- 

 sisting of a short broad spine, with two strong lateral spines, 

 which are crenulated along their inner margins for the at- 

 tachment of tinibria. 



Test thin and without special ornamentation in the typ- 

 ical sjjecies of the genus, which shows only vascular striae 

 along the margins of the valves, and over the segments of 

 the abdomen. 



This genus differs conspicuously from Eciiinocauis in 

 the form and ornanieiitation of the valves, and in the num- 

 ber and character of the segments of the abdomen. In tlie 

 outline of the valves it is very similar to Troimixx^aiiis, 

 and is distinguished by the absence of the strong longi- 

 tudinal ridges presented by the species of that genus. 



Elymocaims SII.IQTTA, 11. SJ). 

 Plate II, Figs. I, 2. 



Carapace i-Hgularly convex, pod-shaped, dorsiil line 

 straight, somewhat shoi't^r tlian the greatest lengili of tlie 

 valves. Valves elongate, longitudinally sub-(puidnnigul:ir 

 or rhomboidal in outline; IfMigtli e(|ual to tnoi'c than twice 

 the greatest widtli. Margins thickened, regularly cui'ving 



