Bkkdk.] Carboniferous Invertebrate*. 85 



front and more abruptly to the beak, generally with a moder- 

 ately distinct mesial sinus ; posterior lateral slopes descending 

 almost vertically to the ears ; umbonal region gibbous, and with 

 strong incurved beak projecting beyond the hinge line. Dorsal 

 valve somewhat flattened in the visceral region, but most con- 

 cave near the beak and near the anterior lateral regions, the 

 concavity widening rapidly forward, so as to leave a kind of a 

 broad, obscure, oblique ridge between it and the flattened ears, 

 and another in the middle ; anterior and lateral margins fol- 

 lowing the curvature of the other valve ; cardinal process 

 prominent, bifid, and rather narrow; interior with mesial 

 ridge, narrow, well defined, extending forward beyond the 

 middle," bifid, at its connection with the cardinal process en- 

 closing a moderately deep pit. The two lateral ridges are well 

 defined and parallel with the hinge, fading out before the ex- 

 tremity is reached. The adductor scars are either subsemicir- 

 cular or spatulate in outline, placed well to the posterior, with 

 the smaller end forward, ending in a small elevated lobe. The 

 brachial markings of this species are very obscure ; they extend 

 from the anterior extremity of the adductor scars outward and 

 a little forward, rounding off near the antero-lateral edge of 

 the flattened area. The markings of the interior of the other 

 valve are rather indistinct. The adductor scars are long, slen- 

 der, subspatulate, with the larger end toward the beak, situated 

 in the middle of the visceral area ; the two are separated in the 

 extreme posterior portion by a low mesial ridge ; exterior to 

 these are the diductor scars, occupying a rather large space, in- 

 dicated by longitudinal folds or nearly parallel lines. "Sur- 

 face of the ventral valve with more or less defined, rather broad 

 concentric undulations, and obscure stria 4 of growth, over the 

 whole of which are arranged two sets of spines, connected at 

 their bases with short interrupted ribs or elongated tubercles. 

 One of these sets consists of small, short, appressed spines, and 

 the other of stout, more erect, long ones. Surface of dorsal 

 valve with small concentric ridges and stria', with many little 

 pits ; spines nearly or quite all small, short, and appressed." 



