JEFFERSON COUNTY. 
395 
105. 
1. Pterinea undata. 3. Strophomena alternata. 5. Nuculites faba. 
2. Nuculites inflata. 4. Oibicula terminalis. 6. Atrypa extans. 
No. 1 . Pterinea undata, is a rare species, found in the grey variety of the trenton at 
Watertown. 
No. 2. Nuculites inflata, is also a rare species, found at Watertown. The trenton is the 
lowest rock in which the genus Pterinea has yet been discovered ; a fact which is interesting, 
inasmuch as this genus furnishes so many species in the rocks of the New-York System. 
No. 3. Strophomena alternata, whose strire or markings are alternately fine and coarse. 
This character is possessed, however, by other species, and hence is not in itself to be relied 
upon as specific. 
No. 4. Orhicula terminalis, is a new species, in the grey trenton at Watertown. Both 
valves are preserved in the specimen from which the drawing was made. It is rare; only 
one specimen has fallen under my notice. 
No. 5. Nuculites faba. This fossil is very abundant at Watertown, in the black irregular- 
bedded limestone. 
No. 6. Atrypa extans, is found at Watertown in the grey limestone, and, at this locality, 
appears to be sufficiently common. I have not, however, seen it elsewhere. 
The Pterinea orbicularis (No. 3, Fig. 109), is found at Watertown, in the black limestone, 
associated with Nuculites and Bellerophon profundus. Though quite common here, it is rare 
to obtain it perfect, as the shell is thin. 
The corallines of the trenton limestone consist of several known genera, each comprising 
but a few species. No. 3 (Fig. 99, p. 389), represents the Puffball favosite, which is pro¬ 
bably as characteristic of this rock as any of which mention has been made. It is found at 
Essex, Plattsburgh, Chazy, Watertown ; in fine, there is no locality of this rock which has. 
not furnished numerous specimens of this fossil. 
