202 Cincinnati Soctety of Natural History. 
This, the typical form of the species, has been seen as yet only 
in the Chester shales at Chester, Ill. What I shall provisionally 
call 
var. CALDWELLENSIS, Nn. var., 
is represented by figures 7 a, 6, c, on plate 14. It occurs at the 
top of the Chester group in Caldwell Co., Ky., and differs from 
the typical ferm in being a little shorter, in having the curve of its 
ends fuller, and only a centrally situated umbilical pit instead of a 
sulcus reaching the dorsal margin. The posterior half is also a lit- 
tle less tumid. 
Size: Length, 0,79 mm.; height, 0.55 mum; thvekmecssyov1s 
mm. 
PRIMITIA SUBHQUATA, N. sp. 
Plate XTVG Fags. 8) 0s ce 
Size: Length, 0.56 mm.; height, 0.34 mm.; thickness of one 
valve, 0.15 mm. 
Valves suboblong, strongly convex, with straight back, rounded 
subequal ends, and uniformly curved ventral edge. Flange illy 
defined, recognizable at the ends only. Umbilical pit central, 
faintly impressed. 
This and the two preceding species are related to the Silurian 
P. humilis, J. and H., but each is distinguished by its own pecul- 
iarities, so that, while I am willing to admit their probable descent 
from that early type, it has seemed desirable, and to the best 
interest of geology, to view them as specifically distinct. In any 
event, they are distinguishable, and therefore deserve recognition 
in our nomenclature. | 
Position and locality: Top of the Chester group, Claxton P. 
O., Caldwell Co., Ky. 
