es ee) 
THE NATURAL HISTORY SURVEY. 399 
ending in a nodule of which the posterior is larger and more 
prominent; nave rather thick, whitish; hinge very stout, list 
strong; cardinal teeth rather large, and strongly projecting in- 
ward from the hinge list; in the right valve one, strongly 
curved, posterior part thick, anterior thin, lamellar, the ends 
united by a lamella soas to form a deep groove into which the 
posterior tooth of the left valve articulates; in the left valve 
two, the posterior (inferior) stout, massive, the other, superior 
and a little anterior, rather short, fine, lamellar, oblique, little 
curved; lateral teeth large, high and pointed in the left, 
strongly projecting inward in the right valve, the latter with 
no (or only traces of) outer teeth, and a deep groove; between 
the cardinal and the lateral teeth the hinge-list is rather deeply 
excavated, so that all teeth are markedly isolated; muscle in- 
sertions visible; ligament short, strong.” (Sterki.) 
Length, 1.90; height, 1.90; breadth, 1.40 mill. 
Ceti Maesteg ore in AEBS 
{Era aris beers hb i: aOare, 
Animal: “Soft parts slightly yellowish.” (Sterki.) 
Distribution: Tuscarawas River, New Philadelphia, Ohio 
(Sterki); Joliet, Ill. (Ferriss); Lilycash Creek (Handwerk). 
Geological distribution: Pleistocene; Lower Loess of IIli- 
NOW, {seerki.)- 2 
Habitat: ‘Living in mud among aquatic plants and dead 
leaves, and as arule covered witha black or brown coat, some- 
times so thick that they appear to be globules of dirt.”’ (Sterki.) 
Remarks: ‘‘The singular shape of the umbones is so char- 
acteristic that this species will be recognized at once, and can- 
not be mistaken for any other. And also in the formation of 
the hinge it is quite unlike any other Pisidium, so that it holds 
a peculiar position in the genus. In the hinge structure it is 
very illustrative and instructive for the understanding of the 
different forms of teeth.” .... 
“Our species is rather variable, even so that all specimens 
from one place in the river are different in size and shape 
from those of another place scarcely half a mile distant. It 
measures from 1.60 to 2.10 mill., I.go0 being about the aver- 
age; the margins may be rather obtuse or somewhat acute, 
the beaks more or less prominent, and the anterior nodule 
more or less marked. Asarule there are no outer lateral teeth 
in the right valve, yet traces of them may be seen in some spec- 
