10 PPP. iiKPoiM- OF I'uor.r.Ess. r. e. beeciier. 



belong to a species orlierwise unknown. In general form 

 tliey are triangular with a broad Hat manubrium for articu- 

 lation or the attacliment of muscles. Inner or masticating 

 side arclied laterally, concave to the dorsal side of the cara- 

 pace. Crown lunate, broadest anterior to the middle, and 

 furnished with a row of usually six, more or less, bicuspid 

 denticles. The denticles become more prominent and acute 

 towards the posterior extremity of the crown, where they 

 are also somewhat oblique, while anteriorly they are 

 broad and obtuse. The test forming the crust of the 

 mandible reaches a thickness of more than one mm. over 

 the denticles, but becomes very thin over the expansions of 

 the sides and on the manubrium. For this reason very few 

 of the specimens preserve more than merely the row of 

 denticles. 



M. J. Barrande has figured and described several speci- 

 mens of a similar nature and has referred them to the 

 genus Ceratiocaris from their association with species of 

 this genus in the Silurian of Bohemia. It is therefore 

 probable that these portions of the animal do not furnish 

 sufficient generic character to be of importance. 



Formation and localities. — In the shales of the Hamilton 

 group ; at Delphi, Pratt's Falls, and the shore of Cayuga 

 lake, New York. 



ECHINOCARIS SOCIALIS, n. Sp. 

 Plate I, Figs. 1-12. 



Carapace convex, obliquely ovate in outline, widest 

 posterior to the middle, length about one-third greater than 

 the width. Dorsal line straight, oblique, having a length 

 of more than one-half the longest diameter of the valves. 

 Margins thickened, carinated, curving outwards over the 

 anterior end of the valves at nearly right angles to the direc- 

 tion of the hinge, continuing in a broad curve to the lower 

 posterior end, where the margin is abruptly rounded, thence 

 extending in nearly a straight line to the hinge. 



Cephalic region triangular in each valve, distinctly lim- 

 ited by a furrow extending from tlie center of the dorsum, 

 curving outwards and downward to the anterior margin, 



