317 



CRUSTACEA. 



AsAPHus Pelops. (N. sp.> 



Fig. 304. Fig. 305. 



Fig. 304. — Asaphus Pelops. a, the pygidium ; b, the hypostoma. 



305. — d ? curiosa. The pygidium. The specimen is somewhat distorted. 



Description. — Pygidium rather strongly and uniformly convex, smooth, 

 no marginal groove ; length two-thirds the width ; anterior angles ob- 

 liquely truncated for about half the width of the side lobes ; an obscure 

 pleural groove just behind the genal angle, and extending thence nearly 

 to the dorsal furrow ; axis about one-third the whole width, scarcely 

 elevated above the general surface ; dorsal furrows only distinguishable 

 near the margin. The widest part of the pygidium is on a line drawn 

 across it at about one-fifth the length from the middle of the front margin. 

 The whole margin behind this line is uniformly curved, forming very nearly 

 a regular semicircle.- In some specimens the middle of the posterior 

 margin shews a tendency to become' more narrowly rounded or obscurely 

 angular. The axis is in general, only distinguishable near the anterior 

 edge. On the under side the fold of the crust, or doublure, is equal to 

 full one-third the whole width of the pygidium. It has a small pit in it 

 near the middle of the posterior margin. 



The hypostoma is short, transversely ovate, its width about one-fifth 

 greater than its length, the alar expansions at the anterior angles small 

 and acute, the notch behind them also small and rounded ; the central 

 portion in the anterior half is gently convex ; the two side lobes flat ; the 

 notch in the posterior margin is shallow, rounded, its depth about one line 

 where the whole length is six lines ; the muscular impressions are rather 

 large, about one-third of the whole width distant from each other, and 

 with their centres a little behind a line drawn across at the mid-length. 



Fragments of the head shew that the posterior angles are rounded 

 angular. The eyes are small, and situated a little behind the mid-length 

 of the glabella. 



