NAPLES FAUNA IN WESTERN NEW YORK, PART 2 263 



are not always present, nor can they be seen on interiors of the most 

 delicately replaced valves. 



Habitat, Genesee province ; Naples subprovince. In the Naples 

 shales at Naples and vicinity. It is not a very common species. 



ACTINOPTERIA Hall. 1 883 



Actinopteria sola sp. nov. 



Plate 12, fig. 20 



Shells small, suberect ; subrhomboidal in outline, hinge line straight, 

 extending to but not beyond the posterior extremity of the valve. Wing 

 moderately broad, set off from the body of the valve by a rather low depres- 

 sion and not extending backward beyond the posterior margin of the valve. 

 Auricle conspicuous, convex in the middle, depressed near the cardinal line 

 and bounded below by a broad sulcus. Beak at the anterior one third of 

 the hinge. Anterior extremity rounded abruptly, outline emarginate at 

 the byssal groove, thence descending at first directly and then more 

 obliquely to near the posterior extremity, to which it curves upward and 

 beyond it inward to the base of the wing. Umbo convex, overarching the 

 hinge ; surface sloping thence gradually to the basal line and more abruptly 

 in front and behind. 



Surface bearing sharply elevated rounded radii, which are simple in the 

 umbonal region and are about 20 in number. At the margin they have 

 increased by intercalation to double this number and cover both auricle 

 and wing, though simple on both these. 



Dimensions. Length 5 mm ; hight 4 mm. 



Habitat. Genesee province ; Naples subprovince. In the soft shales 

 on Cashaqua creek. 



Observations. The single left valve of this species is the only 

 observed instance of the occurrence of this genus in the Naples shales and 

 the diminutive shell looks much like an interloper from the contemporary 

 Ithaca province of the central New York sea. That fauna is specially 

 characterized by the diversity of expressions of Actinopteria, all specifically 

 based on the type of the ancestral A. b o y d i of the fauna preceding this 



