162 
NAT7TIL0IDEA. 
Seven species of Piloceras have now been described, viz. : — 
P. invaginatum, Salter. 
P. Canadense^ Billings. 
P. Wortheni, Billings. 
P. Triton, Billings. 
P. graciU, Billings. 
P. amjglum, Dawson. 
P. explanator, Wbitfield. 
From a geological point of view Piloceras is interesting from its 
association in Scotland and in Eastern North America with a little 
group of fossils in which several species appear to be common to 
both countries. 
Salter enumerates amongst others the following American species 
in the Durness Limestone, some of which, however, are too imperfect 
for accurate identification : — 
Ortliis striatula, Emmons (non Scblothcim). 
Opliileta compacta, Salter. 
Madurea matutina ?, Hall. 
Ortlioceras arciioliratum, Hall. 
0. undidostriatum, Hall. 
0. vertehrcde'l, Hall (very doubtful). 
In addition to these, there are among the fossils I received from 
the Geological Survey of Scotland, specimens of Endoceras in a very 
fragmentary condition, but resembling certain small (?) species with 
very closely approximate septa, described and figured by Billings 
from the Calciferous of Canada b 
A Cyrtoceras, very probably the Oncoceras ? referred to by Salter, 
is also in a condition unfit for determination. 
Though the Durness fossils are by no means well preserved, yet 
it can hardly be disputed that their general facies, as Salter affirmed, 
is American rather than European 
Horizon. Durness Limestone ( = Calciferous (?)of North America). 
Locedity. Durness, Sutherlandshire. 
Fairly well represented in the Collection. 
Piloceras Canadense, Billings. 
1860. Piloceras Canadense, Billings, Canadian Nat. and Geol. vol. v. 
p. 171, f. 16. 
’ Canadian Naturalist, 1859, vol. iv. p. 361. 
^ The bulk of the foregoing observations is contained in my paper pubhshed 
in the ‘ Geological Magazine,’ Dec. 1887, “ On the genus Piloceras.” 
