Weller — Kinderhook Faunal Studies. 163 



sinus ; regularly arched from beak to front, highest in the 

 middle, exhibiting a convexity equal to that of the opposite 

 valve. Muscular scars consisting of a faint but distinct linear 

 median impression, with a much deeper linear impression on 

 each side, and a very faint one exterior to each of these — 

 the three principal impressions reaching to the middle of the 

 valve. Shell thin, stony and solid ; structure beautifully 

 punctate under a lens ; general surface polished, marked by a 

 few feeble concentric lines of growth/' 



Length of type specimen 17 mm., breadth 11 mm., con- 

 vexity of pedicle valve 5 mm. 



Remarks. The type specimens of this species are from bed 

 No. 5 and from the overlying oolitic limestone. The 

 original description of the pedicle valve was made from an 

 internal cast from the sandstone, the brachial valve and the 

 shell structure being described from an oolitic limestone 

 specimen. The specimen illustrated is the type of the pedicle 

 valve. 



In the original description this species was referred to 

 the genus Centronella. The brachidium has never been 

 observed but it is extremely probable that the species is a 

 Dielasma. It is referred to this latter genus here because 

 it has the general form of other members of the genus and 

 does not so closely resemble members of the genus Oen- 

 tronella, 



Spirifer centronatus Win. 



PL XIV. f. 3-4. 



Shell broadly subtriangular in outline, hinge-line extended, 

 with mucronate cardinal extremities, breadth alons: the hinffe- 

 line usually more than twice the length of the shell. Pedicle 

 valve much more convex than the brachial, the greatest con- 

 vexity being at a point in about the middle of the valve, the 

 slopes from this point to the cardinal extremities, concave; 

 beak pointed and incurved; sinus rather narrow, sharply 

 defined and subangular at the beak, becoming rounded to- 

 wards the front, with one median plication starting near the 

 beak and extending without division to the anterior margin ; 

 the bounding plications of the sinus are larger than any others 



