Welter — Kinderhook Faicnal Studies. 83 



surface markings on the anterior ear become nearly obsolete, 

 while on the posterior ear the concentric markings become 

 stronger at the expense of the radiating costae. 



Remarks. The specimens which are labeled as the types of 

 this species in the University of Michigan collection are four 

 in number, two of them being from the Chonopectus sand- 

 tone, the others from a higher horizon. It is altogether prob- 

 able that all these specimens do not belong to a single species, 

 and it is impossible to determine from his description and 

 measurements which one of these specimens Winchell consid- 

 ered as the type. The two species from the Chonopectus 

 sandstone are of the same species, and one of these is here 

 selected to represent the species and the description has been 

 entirely rewritten. 



The specimens from the Waverly series in Ohio, identified 

 as A. caroli by Hall and by Herrick, probably do not belong 

 to this species. 



PTERINOPECTEN. — Cf . P. LAETUS H. 



PI. III. f.1-2. 



Shell 27^- mm. in height, the length about one-fourth 

 greater than the height. Left valve moderately convex ; 

 hinge-line straight, about equal to the greatest length of the 

 shell; pallial margin regularly rounded. Beak scarcely 

 elevated above the hinge-line, located about f of the distance 

 from the anterior extremity. The anterior ear of the left 

 valve depressed, slightly convex, separated from the body of 

 the shell by a shallow and narrow sinus ; its anterior margin 

 rounded above and nearly straight below, meeting the hinge- 

 line at approximately a right angle, joining the pallial margin 

 in a broadly rounded notch. The posterior wing broad and 

 flattened toward the margin, but not sharply separated from 

 the body of the shell; its posterior margin sinuate. The 

 surface of the left valve ornamented with 85-90 rounded, 

 radiating costae, a few of which near the center of the basal 

 margin are smaller than the others and do not extend to the 

 beak. The costae on the anterior ear are finer than those on 

 the body of the shell, and in the sinus separating the ear 

 from the body of the shell they are nearly obsolete. The 



