NAPLES FAUNA IN WESTERN NEW YORK, PART 2 25 I 



sent the more elongate and usual form of the species. All of Hall's figures 

 are of specimens from the Genesee shales. 1 



The surface markings of these shells vary somewhat. Normally the 

 surface was smooth, marked only by fine, crowded growth lines. Many 

 specimens show that in the umbonal region the concentric lines were more 

 regular, sharper, elevated, distant, and distinctly continuous. Under 

 ordinary preservation, however, this regular character is lost before the 

 middle of the valve is reached. All the figures in the Paleontology of 

 New York, v. 5, pt 1, pi. 71, show a concentric striation exceptionally 

 regular, and not to be found on the specimens, with the exception of one, 

 figure 2, taken from a group of shells in the bituminous Genesee shale 

 near Darien N. Y., in which the fine, sharp, regular striation is maintained 

 over the entire surface. 



I have not seen specimens from other localities in which this feature is 

 shown, but it appears to characterize all examples from the locality cited. 

 Radial striae, as we have observed, are not a feature of the exterior. Such 

 striae are not infrequently seen, but they appertain t.o the inner shell layers. 



The byssal ears have not heretofore been correctly represented. In 

 specimens from the shales their outer margins are usually broken off, 

 leaving them narrower in appearance than they actually were. There is no 

 evident difference in size or shape in the flanges of opposite valves ; on the 

 contrary, all testimony confirms their equality in this respect, as well as the 

 equivalvular character of the entire dissoconch. 



Dimensions. Average specimens measure approximately as follows : 

 one from the Marcellus shales is 6 mm in hight and 8 mm in length ; its 

 byssal margin is 5 mm in length. Specimens from the Genesee shales 

 present about the same size and proportions. An average example from 

 the olive Naples shales measures, hight 5 mm, length 7 mm, length of 



1 The large smooth shell, Lunulicardium marcellense Hall, occurring in the 

 interbedded shales of the Agoniatite limestone (Cherry Valley) suggests Pterochaenia in 

 aspect, but* the species appertains rather to the smooth Prochasma forms of Lunuli- 

 cardium, lacking the critical structure of the other genus. 



