832, THE DEVONIAN FOSSILS OF CANADA WEST. 
Genus StropHoponta.—(Hall.) 
In 1847, Mr. Sharpe pointed out that in Strophomena, demissa there. 
was no foramen, and says: ‘It will probably be found to indicate a 
distinct genus, as it must be accompanied with a peculiar internal 
arrangement, Until this can be ascertained this species may remain 
in Leptena, the genus to which it is most closely related.” * 
In 1849, Professor Hall proposed his genus Strophodonta (giving 
S. demissa as the type) founding it on the characters poited out by 
Sharpe, and adding thereto the following remarks on the interior: 
«“ Tn the interior there are no dental lamelle margining or surrounding 
the muscular impressions, which are spread out over a considerable 
surface in the dorsal valve, shewing partially a double or bilateral 
arrangement. In the ventral valve there is some indication of a 
limitation, or marginal elevation, to the muscular impression, but the 
character is quite distinct from the same in Leptena.’+ 
In 1852, Prof. Hall redescribed the genus, founding it upon the 
striated area and closed foramen, but gave no internal characters, 
except, ‘“‘ Muscular impression somewhat bilateral.’ t 
In 1858, Professor Hall, in the Geology of Iowa published the 
following more detailed description of the internal characters : 
“Tn the ventral valve the teeth are much reduced or nearly obsolete, a central 
more or less prominent bilobed process usually occupying the centre of the area 
in place of the triangular fissure of SrropHomena. Muscular impressions 
strongly marked, semielliptical or subreniform, separated in the middle by a 
depressed line, and sometimes margined by a semicircularjridge, which is an 
extension of the lamelle from either side. Vascular impressions foliate or 
flabellate, extending beyond the areas towards the base of the shell. 
“Dorsal valve with the muscular and vascular impressions strongly marked : 
cardinal process bifurcate from the base, with each branch bilobed at the extre- 
mity, by which it is articulated to processes beneath the area of the opposite valve, 
receiving between its forks the cardinal process of the opposite or ventral valve, 
which is bilobed or grooved for the passage of the peduncle. Entire interior 
surface papillose.”§ 
I hold that the above is simply a description of the internal char- 
acters of the genus Strophomena with the exception of the passage 
that I have put in italics, which contains a statement decidedly incor- 
rect. We have a number of specimens of S. demissa, S. inequistri- 
* SHARPE, in Quar. Jour. Geol. Society. Vol. 6, p. 172. 
+ Hatt. In Proc. Am. Ass. 1850, p. 348. 
= Pal. N, Y. Vol. 2, p. 63. 
§ Haut. Geology of Iowa. Vol, 1., Paré 2, p. 491. 
