THE DEVONIAN FOSSILS OF CANADA WEST. 267 
there are other imperfect specimens from two inches to two inches and 
a half in width, which I have no doubt belong to the species. 
The inclination of the area of the ventral valve, judging from several 
fragments that I have examined, appears to vary considerably. 
This species belongs to that group of the genus of which O. umdra- 
culum (Schlotheim) is a characteristic form. Mr. Davidson has recently 
placed the species of this type in the gems Streptorhyucus (King) 
with the followmg remark: “‘The shells composing this sub-genus, 
are closely related to Strophomena; they are usually semicircular, 
conyex or concayo-convex, and externally striated ; the ventral valve 
possessing a prolonged and oftentimes bent or twisted beak.’”’— 
(Grotoerst, March, 1860.) The species vary greatly im size and 
form, and Mr. Davidson has, therefore, united under one name (S. 
crenistria) no less than twelve varieties, which have all been considered 
to be distinct by various authors. Our fossil closely resembles S. 
crenistria in external form, but differs im not having the radiating 
striz crenulated, and further in the form of the occlusor muscular 
impressions in the dorsal valve. According to Davidson’s figure, 
there is a small process between the two branches of the cardinal 
process of the dorsal valve, which does not exist in ours. [I shall give 
some further illustrations of this species hereafter. It is only since 
this article was sent to the press that I have procured specimens which 
exhibit the interior of both valves. 
Locality and formation.—Lot No. 6, Con. 4, Townsend. Also at 
Rama’s farm, near Port Colborne, and near Woodstock. 
Collectors.—A. Murray, E. Billings and J. De Cew. 
Orruis Livia.—J. Sp 
Fig. 14. Fig. 15. Fig. 16, 
Fig. 14, Orthis Livia.—Ventral valve, Fig. 15.—Longitudinal section of the same. 
Fig. 16.—Dorsal valve. F 
