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 lowa 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, Lowa, 
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 strize 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 striz. The presence of fine radiating strie 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 striz 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- 
llcDw 
