CRUSTACEA. 175 



Hinge-line short, straight; anterior margin curving somewhat abruptly for 

 a short distance, thence broadly rounding to the postero-ventral edge, there 

 curving abruptly forward and passing in a nearly straight line to the poste- 

 rior extremity of the hinge. Margins distinctly and sharply elevated on all 

 except the dorsal side. 



Nuchal furrow scarcely distinct, cutting oil* a sub-triangular area on each 

 valve, similar in relative proportions to that in E. punctata. 



The Cephalic region occupies about one-fourth the area of each valve, and 

 its surface is mostly covered by a single large, elevated node, irregular in 

 outline and when uncompressed, merging into one inconspicuous node lying 

 near the dorso-lateral angle, another on the hinge-line at the nuchal furrow, 

 and a third just opposite the nodiform termination of the lower thoracic carina. 



The Thoracic region bears two conspicuous nodes, one near the hinge-line, 

 apparently continuous with the sharply elevated dorso-lateral margin, the 

 other situated medially, abutting closely upon and often apparently con- 

 tinuous with the lower carina. This carina lies at a little more than one- 

 third the width of the valve from the ventral margin, takes its origin at or 

 upon the median thoracic node and passes backward in a broad curve, be- 

 coming extinct considerably within the postero-lateral margin. At a little 

 more than one-half the distance between this carina and the hinge-line, 

 there is a short, straight, or dorsally curved carinate row of sharp pustules. 

 The postero-dorsal margin is also sharply elevated and sub-carinate near 

 the hinge. 



The Surface of the carapace is covered with sharp, sub-spiniform pustules on 

 its elevated portions, the depressed areas being smooth or minutely punctate. 



Abdomen composed of six somites, which become more elongate in outline 

 toward the caudal-plate. Somites sub-cylindrical, bearing three transverse 

 rows of posteriorly directed spinules. The first row of these lies just within 

 the anterior margin ; the second about midway across the segment, and the 

 third at the posterior margin. The spinules of the first row are often 

 inconspicuous. 



