J. W. Salter on Fossils from the Ottawa River. 231 
like a Delphinula ; the third is the very common S. (Huompha- 
lus) uniangulatus above mentioned, which also, but rarely, shows 
atendency to become spinose. There are also two or three 
species of the genus Raphistoma, which appears to be only a dis- 
coid form of Scalites. We have a Twurritella? spirally ribbed, 
and undistinguishable in general form from living species. But the 
most abundant and characteristic shell is the Maclurea, fragments 
of which, with scattered opercula, occur on almost every surface. 
Among bivalve shells, which chiefly belong to the Arcacide, 
a very interesting new genus has rewarded examination. It was 
found that two species resembling Nucula in every general cha- 
racter, differed from it importantly by having no internal ligament, 
but a very manifest exterior one; one of these species measures 
three inches across, and from the general analogy of several ac- 
companying species it is believed that this form will be found 
common in the Silurian rocks, and will include many species now 
referred to Nucula. It might be called Céenodonta. Of the same 
family also, a Lyrodesma (a genus with radiating teeth beneath 
the beak and synonymous with Actinodonta, Phillips) is closely 
allied to a Trenton limestone species. ‘There is a new genus, 
probably belonging to the Arcacide, but only possessing two or 
three anterior teeth ; but the collection does not include any Avi- 
cule, or indeed any other of the usual Silurian genera of this or- 
der, and of the seven or eight lamellibranchiate shells none appear 
quite identical with those from New York; but, as might be ex- 
pected, the common Brachiopoda of this locality are those most 
abundant also in the Trenton limestone. Orthis tricenaria, Con- 
rad, swarms here, as does also Leptena filitexta, Hall, a shell very 
like the common J. alternata of the Trenton limestone, but re- 
versed as to the convexity of the respective valves. But the latter 
shell,so abundant in New York, does not occur here at all. 
Atrypa hemiplicata, Hall, and A. increbrescens are tolerably fre- 
quent ; and there are two or three other species of Orthis, and 
Some small plaited and smooth T'erebratule, which require fur- 
ther examination. see ; 
The Bellerophons, two of which are probably identical with . 
New York species, are those of the lowest or chazy limestone, 
namely, B. (Bucania) sulcatina, Emmons, and B. rotundata, 
Hall. "'The group to which these two belong is that of which 
Perhaps one of the most interesting of the mollusks is a large 
Jleodora, quite new to America, and not yet described as such 
from Britain. On attentively comparing the American, Irish and 
