CRUSTACEA. 179 



the postero-dorsal margin, which is nearly straight. The entire margin is 

 elevated and is especially strong upon the posterior portion. 



Nuchal furrow quite conspicuous, directed obliquely forward from the 

 hinge-line. 



Cephalic region apparently sub-triangular upon each valve and elevated 

 into a conspicuous node, the surface of which is covered with sharp, scat- 

 tered tubercles. 



Thoracic region characterized by an arrangement of nodes similar to that 

 observed in Echinocaris sublavis : a transverse dorsal node, just behind the 

 nuchal furrow, directed slightly forward, followed below by a second trans- 

 verse, elongated node, produced backward into a faintly curving ridge or 

 carina, which becomes obsolete on the posterior area of the carapace. The 

 postero-dorsal area is convex and relatively small. The surface of the thoracic 

 nodes and of the postero-dorsal area is covered with conspicuous tubercles, 

 while the remainder of the test appears to be minutely punctate or granulose. 

 Length of the carapace 13 mm., width 9 mm. 



Abdomen and Post-abdomen not observed. 



Observations. A single valve of the carapace of this species has been observed, 

 and, in the disposition of the nodes and ridges upon the surface, it shows a 

 close resemblance to its associate in the same formation, Echinocaris sublavis. 

 E. pustulosa, however, differs from that species in the less oblique outline of the 

 carapace, and the more centrally situated lateral carina. It resembles E. socialis 

 in its strongly tubercled surface, but the differences in these two species are 

 readily apparent. 



Distribution. In the calcareous concretions of the Erie shales ; LeRoy, Lake 

 county, Ohio. 



