S Wo Pord=The' Genus Obdtella: 131 
Art. XVII.— Remarks on the Genus Obolella ; by S. W. Forp. 
THE genus Obolella was founded by Mr. Billings, in 1861, 
upon three smal! Linguloid species, namely O. chromatica from 
the north shore of the Straits of Belle Isle, O. crassa from Troy, 
., and O. polita from the Potsdam sandstone of Wisconsin, 
cm ig. 1.—Diagram of the interior of the ventral valve of O. crassa, enlarged two 
diameters. Fig. 2.Diagram of the interior of the dorsal valve,”enlarged to the 
NY degree, The specimens are from the original locality of the species, Troy, 
As a rule, the beak of the dorsal valve is curved downward so 
as to almost touch the short, indistinct hinge-line, while that of 
the ventral valve is less depressed and slightly more projecting ; 
and these are the only features by which the two valves ma 
be externally distinguished. The majority of the specimens 
of the ventral valve have an extremely shallow depression run- 
ning from the beak to the anterior margin along the median 
line; but I have found that even this is not distinctive, inas- 
much as some of the dorsal valves exhibit it. The specimens 
* This Journal for March, 1876. 
