FOSSILS OF THE DEVONIAN. 



161 



found that the three varieties were united by a series of specimens having 

 intermediate characters between the extremes I had designated as distinct 

 species. On- examining the interiors of the valves of the Iowa and Nevada 

 shells, they were found to be similar; also the area, which is of a variable 

 character. In a beautiful series of specimens from Independence, Iowa, 

 received from Professor Calvin, the area of the ventral valve varies greatly 

 in extent and height, and many of them showed no more of a decided area 

 than specimens of P. galeatus, now before me, from the Lower Helderberg 

 Group of Albany County, New York. On one of Professor Calvin's speci- 

 mens from Solon, Iowa, the area appears to be vertically striated, but a close 

 examination shows this to have originated from the scratching of the tool 

 used in cleaning away the matrix. All other specimens from Iowa and Ne- 

 vada showing the area intact, are transversely striated. When the area is 

 not well defined the striae of growth arch around the rounded lateral margins 

 and reach in to the edges of the vertical fissure. Professor Hall describes 

 the area as vertically striated; we have failed to find any specimens showing 

 the vertical striae. The presence of fine radiating striae is not mentioned 

 either by Owen, Hall, or Meek and Worthen, but they are present on speci- 

 mens from Davenport, Troy Mills, and Independence, Iowa, and the Eureka 

 District, Nevada. Concentric striae are also well defined on many speci- 

 mens, while others show little more than a smooth surface. 



I think the identification of this species by Meek and Worthen with that 

 of Owen is correct, and it also establishes a specific name, as the genus Gyp- 

 idula Hall, does not appear to have good generic characters to distinguish 

 it from typical forms of Pentamerus, and if the species is referred back to 

 the latter genus, the name occidentalis cannot be used owing to its being pre- 

 occupied. 



Pentamerus Lotis, n. sp. 

 Plate iii, figs. 9, 9a-c. 



Shell small, subglobose, transverse or with the height and width sub- 

 equal. 



Dorsal valve deeper and more convex than the ventral; regularly 

 arched from beak to front, with a strongly marked somewhat flattened me- 

 11 o D w 



