336 “THE “DEVONIAN FOSSILS OF CANADA WEST. 
SrropHOMENA RHOMBOIDALIS.—(Wahlenburg). 
LerreNna DEpRESSA + STROPHOMENA DEPRESSA + LepTHZNA 
RuGOSA + STROPHOMENA RUGOSA + LEPTHNA TENUISTRIA- 
TA?’ + PropuctTa pEPRESSA + P. ANALOGA, &c. Either 
wholly or in part, of the generality of authors.* 
SJ 
PO 
WwW 
Fig. 112. 
Fig. 111. 
Fig. 111.—Strophomena rhomboidalis, with the front straight. 
Fig. 112.—The same with rounded front. 
Description Rhomboidal or irregularly semi-oval, widest on the 
hinge-line, occasionally somewhat square: visceral disc strongly 
corrugated by from nine to fifteen deep undulating concentric wrin- 
kles ; both valves abruptly bent at one-half or two-thirds the length 
to form a broad margin deflected towards the dorsal side. In the 
ventral or convex valve the disc is nearly flat, but with a small portion 
in front of the beak gently tumid. The curvature of the dorsal 
valve conforms very nearly to that of the ventral. Area of ventral 
valve narrow, seldom exceeding half a line in width; the dorsal area 
still narrower ; the two areas inclined towards each other at an angle 
which varies from 30° to 60°. Foramen of yentral valve large, 
triangular, wider than high, partly filled by the two projecting extre- 
mities of the divaricator processes of the dorsal valve. Surface 
covered with fine crowded striz of a nearly equal size throughout, 
five or six in the width of one line. 
In the interior of the ventral valve the muscular impressions occupy 
a subcircular cavity which is about one-third the length of the valve 
and is bordered by an angular slightly elevated margin. The divari- 
* Prof. Hall is desirous of having this species called S. rugosa, and says that he has seen 
specimens of it labelled under that name in Rafinesque’s hand-writing. But according to 
the laws of scientific nomenclature, manuscript names cannot be recognized atall. The 
first published specific name is (rhomboidalis), and this must be retained. The figure of 
S. rugosa, published by De Blainviile as the type of the genus, in 1825, in the Manuel de 
Malacologie, certainly does not represent this species. 
