NOTES ON PALEOZOIC CRUSTACEANS 89 



Genus pseudoniscus Nieszkowski 

 Pseudoniscus roosevelti sp. nov. 



Entire individual subovate, broadest in front, posterior ex- 

 tremity extending beyond marginal curve. 



Head relatively very large, covering nearly or quite one half the 

 entire length of the animal. The marginal curve is sub-semiei lip- 

 tic, the posterior or nuchal curve gently concave, transverse in the 

 middle. The general form^ of the head is thus like an elongate 

 Limulus shield, with sharp sipinee extending from the genal angles 

 and reaching to 'the third segment. In the two entire individuails 

 the head-shield has been but little compressed, and the relative 

 proportions are doubtless more correctly expressed than in some 

 of the detached shields which lie in the more shaly portions of the 

 rock, where flattening has exaggerated the transverse dimension. 

 The anterior and lateral margins of the head bear a thickened 

 edge due to 'the infolding 'or doublure, Vhich makes a fine thread- 

 like line of thickening on the lo'wer side of the carapace. This line 

 follows the lateral margins at a distance of a fraction of a milli- 

 meter within it. At the middle point of the anterior margin is a 

 projecting point, or small angle, and several specimens show that 

 the lateral branches of the thickened thread on the under side 

 approach each other and unite with the margin itself at the apex 

 of this angle. It is not altogether clear whether this line of the 

 doublure, traceable on nearly all the specimens, is actually its 

 innermost edge or marks rather the position of a submarginal 

 suture. The posterior margin of the shield bears between the 

 genal angles and the median portion juxtaposed to the abdominal 

 axis, a series of crenulations which lies within the margin to such 

 a degree as not to interrupt it, but extends on the surface of the 

 head suflSciently to make a notable lornamentation of an otherwise 

 unmodified exterior. Over the median area these fine crenula- 

 tions are replaced by a slight transverse marginal ridge, which 

 appears like a slight " tuck " or " pucker " at the edge of the 

 shield. In other than these features the surface of the shield 

 is not medified. In all the specimens studied there is no evidence 

 that can be construed as indicating the position or presencr^ of 



