CONTEIBUnONS TO PAL^ONTOLOGT. 



137 



CRUSTACEA. 



GENUS DIKELOCEPHALUS (Owen). 



" Cephalic shield semicircular and rather flat. Glabella moderate- 

 "ly convex, equally wide throughout, rounded in front, divided 

 *' by two furrows into three distinct lobes : these well-marked 

 ^' furrows extend quite across the glabella, and form a curve or 

 ^* slightly obtuse angle in the median line directed backwards, 

 ** The anterior lobe is partially divided by a third obscure 

 *' furrow, which becomes obsolete in the median line, 



" Facial sutures distinct, originating in the anterior [posterior] 

 " border of the cephalic shield : they run at first parallel with 

 *' the same ; then convergieg in a sigmoid flexure around the 

 '' eye-plate, diverge again in curved lines, until, reaching the 

 ^' anterior border, they circumscribe an area of greater or less 

 *' extent in front of the glabella. 



" The cheek-plates produced at their anterior [posterior] corners 

 '* into spines of moderate length, 



^'Pygidium rather deeper and about the same width as the ce- 

 ** phalic shield, with from four to six segments ; the last and 

 " largest segment sometimes obscurely subdivided by a faint 

 " furrow. Lateral and interlateral segments blended into a 

 " marginal flap or border of greater or less extent : usually, if 

 *' not always, provided with caudal spines." 



In the form and expression of the glabella, there is considerable 

 resemblance to Paeadoxides, except that it is not expanded in 

 front. The direction of the facial suture, however, is conspicuous- 

 ly different. The extended frontal limb in the typical species does 

 not appear to be a generic feature ; for in the D. pepinensis of 

 Owen it is narrow and convex. The thoracic articulations are 

 marked by a simple groove running out at the lower margin of 

 the distal extremity, which is pointed backwards. The hypostomse 

 associated with D. minnesotensis are very similar to the hypostomse 

 of Paradoxides. In the B. pepmensis we have a facial suture as in 

 D. minnesotensis^ with a narrow convex frontal limb ; while the 

 pygidium is narrow, prominently convex in the axis, with a plain 

 border of moderate width. 



[Senate, No. 115.] 18 



