CRUSTACEA. 189 



pentagonal on the dorsal surface and produced into a relatively narrow 

 telson, shorter than the lateral spines and strongly carinate along the axial 

 line. The lateral spines are flat and long, with a low carina near the inner 

 edge and a series of obscure, parallel ridges near the outer margin. 



The surface is marked by elevated lines, parallel to the margins, and simi- 

 lar to those observed upon the abdomen, but more continuous. Strong 

 tubercles are scattered irregularly over the surface of all the spines. A broad 

 fimbria of setas is visible upon the inner edges of the lateral spines, and the 

 margin is distinctly crenulate for their insertion. 



Dimensions. The largest carapace observed is represented by a right valve, 

 which measures 140 mm. in length, inclusive of the posterior spine, and 60 

 mm. in greatest width. The smallest right valve has a length of 68 mm. 

 and a width of 40 mm. The abdomen and post-abdomen of a large individual 

 measure 105 mm. in length to the apex of the telson: the first somite, 16 

 mm.; the second, 22 mm.; the caudal plate and telson, 67 mm. The cerco- 

 pods of the same specimen are 70 mm. in length. 



Observations. The character of the articulation of the valves of the carapace 

 in this species is widely different from that in typical species of the genus 

 Dithyrocaris. If the valves came into contact only at the apices of the con- 

 spicuous angles upon the dorsal line a long posterior median cleft would be left 

 between the valves with a width equal to that of the anterior or rostral cleft. 

 Three right valves have been preserved showing this angle upon the hinge, but 

 the only left valve observed has been broken at that point. If the process 

 existed on both valves, as we must assume to be true in the bilaterally 

 symmetrical carapaces, it is difficult to conceive how the articulation could 

 have been effected by the mere apical contact of the valves at this point. 

 Upon the right valve the angular extension is smooth near its apex, and the 

 outer edge folded upward into a low ridge, so that it may have been slightly 

 overlapped by and articulated to the valve at this point, but such articulation 

 must have been quite insufficient to hold the two valves in place. With 

 the exception of the surface about the apex, these extensions are quite 



