As regards the internal characters of this species, according to Professor Hall, ‘in 
the interior of the ventral valve, the occlusor muscular impressions occupy a narrow, sub- 
quadrangular elevated space, just beneath the apex, whilst the divaricator muscular imprints 
occupy a short broad space on each side, and are limited by nearly vertical or slightly 
curving ridges which have in some degree the appearance of dental lamellee ; within the limits 
of these ridges the muscular imprints are not strongly marked. In the dorsal valve the pos- 
terior occlusor imprints are broad and extending far towards the cardinal line, and often limited 
externally by alow pustulose ridge; the anterior impressions are small and narrow, separated 
by a narrow mesial ridge, and margined by diverging elevated ridges, which, above the impres- 
sion, are united in the mesial ridge from which proceeds the bifurcating cardinal process.” 
S. inequistriata is- placed by Hall in his genus Strophodonta, and is stated to possess no 
foramen ; but Mr. Billings asserts that a small linear foramen is present. In most respects 
S. inequistriata appears to be identical, as pointed out by Hall, with Leptwna (Orthis) inter- 
strialis, (Phillips), from the Middle Devonian of England and Europe; and no other distinct- 
ons can be at present laid down between the two forms, except that the latter is upon the whole 
somewhat smaller, and that it does not seem to possess the fine concentric strize of the former. 
When the internal characters of ZL. interstrialis are known, other differences may perhaps 
appear. It may also be doubted, as pointed out by Mr. Billings, if 8. incquistriata is specifically 
distinct from the Devonian forms described by Hall under the names of S. fextilis and S. con- 
cava. Lastly, S. inequistriata is closely allied to the S. varistriata of the Lower Helderberg 
Rocks, and has decided affinities with the still more ancient S. alternata of the Lower Silurian. 
“Iam unable to see that there are any differences of specific value between this and S, 
inequiradiata Hall, though the opposite is maintained by Hall. S. inequistriata may in 
general be readily recognized by the characters of its surface-ornamentation and by its shape. 
Locality and Formation.—Corniferous Limestone, Port Colborne; Lot 6, Con. 1, Wain- 
fleet ; Ridgeway, and generally throughout the Corniferous and Hamilton formations of Western 
Ontario. 
79. STROPHOMENA PATERSONI (Hall). 
Strophomena Patersoni (Hall), Tenth Report on the State Cabinet, p. 114. 
Strophomena FPatersoni (Billings), Jour. Can. Institute, New Series, Vol. VI., p. 340, 
Fig. 115. 
Shell semi-oval, ventral valve convex, depressed towards the cardinal angles, which are 
slightly extended or auriculate. ‘‘ Surface marked by distant elevated radiating striz, and 
the intermediate spaces by undulating fine striz, and crossed by short abruptly arching 
wrinkles, which are interrupted by the strong radiating strie. The finer radiating striz on the 
ventral valve are from three to ten or twelve between the stronger ones ; whilst on the dorsal 
valve the spaces are wider, and there are from ten to twenty finer strize between the stronger 
ones, The finer striz are crossed by equally fine concentric striz, giving the entire surface 
a delicately cancellated appearance,” (Hail, Pal. N. Y., Vol. 1V., p. 89). 
S. Patersoni is very closely allied to S. inequistriata, from which it is perhaps not speci- 
fically distinct. The chief points of distinction are to be found in the smaller convexity of 
the ventral valve in S. Patersoni, in the greater number of the fine intermediate striz, and 
in the presence of weil-marked concentric wrinkles. S. Paterson is also allied to the Silu- 
rian S. corrugata of Portlock, but the latter is a flatter and smaller form. 
Locality and Formation.—Not uncommon in the Corniferous Limestone of Ridgeway, 
and Lot 6, Con. 1, Wainfleet. 
80. STROPHOMENA AMPLA (Hall). 
Strophomena ampla (Hall), Tenth Report on the State Cabinet, p. 111. 
Strophomena ampla (Billings), Jowr. Can. Institute, New Series, Vol. VI., p. 345. 
Strophodonta ampla (Hall), Pal. N. Y., Vol. 1V., p. 93, Pl. XIV., 1 a—1 i. 
Shell large, from two to three inches wide, the length from a fourth to a third less, 
semi-oval or semi-circular, the hinge-line as wide or wider than the greatest width of the shell 
below. Ventral valve concave, with a slight convexity near the beak ; dorsal valve convex, 
with a concavity in the neighbourhood of the beak, following the curvature of the ventral 
