NATURAL SCIENCES OF PHILADELPHIA. 179 



Specificallj^, it seems to be more neni'ly allied to Aviculopeden 

 neglectus { = Pecten neglectus^ Geinitz) from the Coal-measures, 

 than to any other form known to me. It has much the same 

 form, and agrees in having the body part of both valves smooth, 

 and the ears costated, or at any rate the anterior one of the right 

 valve. It has a rather shorter hinge, however, more convex 

 valves, and a rather more rounded general outline, with less deeply 

 sinuous margins under the ears; while it attains a somewhat 

 larger size. It may be regarded as the Lower Carboniferous rep- 

 resentative of that Coal-measure species, as many of the other 

 forms from this horizon represent species in the Coal-measures. 



The specific name is given in honor of Dr. G. A. Williams, of 

 Boonville, Missouri, to whom I am indebted for the tj'pical 

 specimens. 



Locality and position. Chouteau Springs, Boon County, Mis- 

 souri; from the beds called the Chouteau Limestone in the Geo- 

 logical Reports of that State, but now known to belong to the 

 same horizon as the upper part of the Waverley group of Ohio. 



SPIRIFER (TEIGONOTRETA?) TEX ANUS, Meek. 



Shell scarcely attaining a medium size, ver}' gibbous in the 

 adult, varying from subquadrate or subglobose to longitudinally 

 subovate, the widest part being generally in advance of the middle, 

 and the length greater than the breadth ; hinge line short, or in 

 young individuals scarcely equalling the breadth of the valves, and 

 in the adult often proportionally very decidedly shorter, some- 

 times obtusely angular at the extremities, while in the more gib- 

 bous individuals its extremities do not project be3'ond the lateral 

 slopes; anterior margin often somewhat emarginate in the middle. 

 Dorsal valve truncato-subcircular or subquadrate and moderately 

 convex; beak incurved with the narrow area, but not prominent ; 

 mesial elevation commencing as a small simple plication at the 

 beak, but rapidly widening and becoming more prominent and 

 angular, with, on each side, several small costre, which divide so 

 as to form altogether 14 to 16 at the front; lateral slopes having 

 at the beak each two or three plications or costae, which farther 

 forward divide so as to form as many fascicles, beyond which the 

 costae become uniform, smaller, and number about 9 on each side 



isn.] 



