Beede.] Carboniferous Invertebrates. 61 



a process from the cardinal process of the brachial valve. 

 Cardinal process of the brachial valve large, elongated, and 

 expanded laterally, divided by a deep sinus at the summit, 

 each lateral lobe having a very deep groove on its posterior 

 side extending nearly its entire length. The cardinal process 

 is very strongly recurved backwards, fitting closely into the 

 deltidium of opposite valve, and backing the process on either 

 side are two high plates extending well back into the visceral 

 cavity, and attached to the brachial valve. Measurements : 

 Length (hinge to front), 45 mm. ; width, 58 mm. ; convexity 

 (maximum), 39 mm.; length of hinge, 35 mm.; height of 

 area, 13 mm. 



Range and distribution : Upper Coal Measures, and base of 

 Permian? Kansas City, Cambridge, Cowley county. 



This species can be easily recognized and separated from the 

 preceding by its larger size, relatively lower beak (as a rule), 

 and its non-bilobate brachial valve. Hall and Clarke have 

 described another species from Kansas City, D. affinis, which 

 is, to say the least, exceedingly closely related to D. cymbula, 

 the principal difference being in the location of the point of 

 greatest convexity in the pedicle valve and smaller size. So 

 far as the topography of the pedicle valve is concerned in this 

 genus, except, perhaps, the relative length and height of the 

 hinge area, it seems to be governed largely by the immediate 

 surroundings of the individual. The location of the point of 

 greatest convexity, and, even as to whether or not there is a 

 concavity in the valve, vary greatly in those species which 

 have a convex or raised valve. In the specimens of D. cymbula 

 in our collection I find no two with the same topography of the 

 pedicle valve, and they vary from regularly convex from the 

 apex of the beak to the extreme front margin to irregularly 

 concave over the same area. Some are regular in their growth, 

 while others are very irregular. It seems to me that the speci- 

 mens described as D. affinis are young or stunted forms of D. 

 cymbula, for it is almost impossible to separate the two forms 

 at all. if we possess the specimens of the two species, and we 

 have specimens that answer the descriptions very closely. 



