BEEDE: UPPER PERMIAN RED BEDS. 159 



The only distinctions between this species and A. occiden- 

 talis Shumard are the (frequently) smaller angle of the 

 beak, which is a little more projecting, the extreme scaly ap- 

 pearance of the anterior ear, and the more pronounced char- 

 acter of the concentric lamellae of the body of the shell. In 

 old specimens some of the costse become somewhat enlarged, 

 as in ^. vanvleeti, but there is little danger of confusing it 

 with that species. 



AVICULOPECTEN VANVLEETI Beede. 



Plate V, flgares 2-2p. 



Aviculopecten vanvleeti Beede, Inv. Fauna Red Beds, p. 6, pi. I, fig. 

 8, 1902. 



Shell large, of variable form. Ears well developed, dis- 

 tinct and prominent. The outline of the shell is much the 

 same as in ^. maccoyi, and the surface marks are similar in 

 most respects. The beaks are prominent and elevated above 

 the hinge, gibbous. Hinge nearly straight, about three- 

 fourths the length of the shell ; anterior ear convex, sepa- 

 rated from the umbo by a deep sulcus, and the anterior 

 margin is deeply sinuate on its lower side. Posterior ear 

 nearly fiat, about as long as the anterior one, separated from 

 the umbo by a less distinct sulcus, and the posterior margin 

 is made gently sinuate by it. The surface is marked by two- 

 ranked radiating costse. Three to six of these are much 

 larger, and appear to be nodular in the cast, probably 

 caused by vaulted lamellae. Between each of these are six 

 to fifteen smaller, rather sinuous, striae, which increase by 

 implantation, and are rounded, low, separated by interspaces 

 equal to their width, and crossed by concentric lamellar 

 markings and larger varices of growth. The larger costse do 

 not become well developed until 15 or 20 mm. from the 

 point of the beak, though they are usually traceable nearly 

 to the point. No specimen before me possesses both ears, 

 but one specimen possesses a posterior ear with five longi- 

 tudinal striae, while another individual shows eight or ten 

 ribs bending downward on the anterior ear. 



Whitehorse spring, Oklahoma ; common. Dozier, Tex. ; 

 rare. 



This species can be distinguished from A. maccoyi Meek 



