NAPLES FAUNA IN WESTERN NEW YORK, PART 2 265 



Of the three shells mentioned, it is quite clear that one (P. h i a n s, 

 originally described as Avicula hians 1 ) has as little relation to the 

 other species as they all have to the type, Posidonia becheri. 

 P. h i a n s, an upper Middle and lower Upper Devonic shell, is of the size 

 of Pterochaenia, with the outline, thin shell, smooth concentric surface of 

 that genus, and also has elongated byssal flanges which are relatively broad 

 at the top, convex and gaping. The posterior cardinal end is rounded. 

 Williams has described as Pterinopecten? atticus from the Naples 

 shales of Wyoming county a species which suggests Posidonia hians 

 and hence the genus Pterochaenia in many of its features, but its sculpture 

 is of so unusual character that it seems judicious to apply to it the same 

 noncommittal generic designation that has been used for somewhat similar 

 fossils, for it is evident that the shell does not appertain to Pterinopecten. 



Posidonia attica Williams (sp.) 



Plate 12, fig. 10-15 



Pterinopecten? atticus Williams, U. S. Geol. Sur. Bui. 41. 1887. p. 35, 

 pi. 3, fig. 10, 11 



Shells small, equivalve, very thin, subquadrate in outline when undis- 

 torted. Beaks minute, prosogyre, anterior, separated from the byssal flange 

 or auricle by a groove which is sometimes well defined and sometimes 

 obscure. Margin of flange convex on cardinal line, incurved and arched on 

 anterior margin, fusing with the body of the shell above the basal margin, 

 which is transverse. Posteriorly the margin is rather abruptly rounded to 

 the cardinal line, at which the angle may be more or less sharp. Beak 

 acute, umbo convex, long and oblique ; slopes in front and behind moder- 

 ately abrupt. The surface of the beaks is smooth, but, soon after secondary 

 growth begins a series of fine ribs develops over the median portion of the 

 valve and increases in size and number to the basal margin. These ribs do 

 not extend over either the anterior or posterior parts of the valve, which 

 are quite smooth, but are restricted to the median portions. They are 



1 Waldschmidt. Zeitschr. def deutsch. geolog. Gesellsch. 1885. p. 924, pi. 40, fig. 4. 



