88 
Corniferous Limestone, and present a very characteristic appearance. The umbonal region of 
the cast exhibits the filling up of the rostral cavity, in the form of a sub-cylindrical or tongue- 
shaped projection, which is usually grooved on its upper surface, and which is bounded later- 
ally by the deep fissures left by the dental lamellz. In front the cast of the rostral cavity 
passes into a great hump or abrupt prominence formed by the cast of the muscular impression. 
The umbonal slope of this prominence is smooth,,and has a median ridge running into the 
rostral cast ; and the front slop is conspicuously striated with longitudinal strize, and often 
divided into two halves by a mesial ridge. 
_ The interior of the dorsal valve shows 
a strong cardinal process, with a shallow 
‘ spoon-shaped depression in the centre, mar- 
gined by deep teeth sockets. The muscular 
area is elongate-ovate, broader above, and 
divided through the centre by a thin ele- 
vated septum. . . . The crura appar- 
ently bend downwards from near their 
origin; thence recurving, they follow very 
a “4 closely the contour of the dorsal valve, 
making thirteen or more turns in an indivi- 
a. Cast of the interior of a eral valve of Athyris nasuta oan pe ua Spires, head 
(Conrad), from the Corniferous TA KCREORE (Original) ; i Interior of simple " (Hall, Pal. New Yo ork, Val., Ve 
the ventral valve of the same (after Billings). p. 301). 
Locality and Formation.—Common in the Corniferous Limestone of Port Colborne and 
Hagersville. 
106. ATHyrRis(?) Mara (Billings). 
Athyris Maia (Billings), Canadian Journal, New Series, Vol. V., p. 276, Figs. 33, 34. 
(2) Spirifera Maia (Hall), Pal. New York, Vol. IV., Plate XLIIL., Figs. 6-13. 
Shell broadly ovate, or sub-rhomboidal ; valves convex, the ventral valve most so. Ventral 
valve strongly convex, exceedingly gibbous in the umbonal region, the beak prominent and 
strongly incurved, but not touching the surface of the dorsal valve ; a shallow rounded mesial 
sinus extending from the beak to the front margin, where it is produced into a linguiform 
extension. Dorsal valve moderately convex, with a small beak, and a rounded mesial fold 
which sometimes extends to beak or sometimes falls short of this point. Hinge-line short and 
straight, the cardinal angles rounded. Surface nearly smooth, with a few lines of growth, and 
in well preserved specimens, numerous fine and close-set concentric striz. 
According to Billings, there exists ‘‘a short false area”? beneath the beak of the ventral 
valve, a feature which our specimens do not enable me to confirm, as the space below the in- 
curved beak is generally concealed by adherent matrix. 
The dimensions of an individual of medium size are as follows:—Length, one inch and a 
quarter; greatest width, fourteen lines, at a point a little in front of the middle; depth, ten 
lines. Larger individuals than the above are of by no means uncommon occurrence. 
Hall has described and figured (Joc. cit.) under the name of Spirifera Maia, a shell which 
he believes to be identical with Athyris Maia of Billings, to which it presents a strong resem- 
blance in its general shape. According to Hall, Spirifera Maia has a narrow cardinal area, 
which is sometimes hidden by the beak, whilst there exists a moderate but conspicuous 
fissure of a subtriangular shape beneath the beak of the ventral valve. Neither of these 
features are alluded to by Mr. Billings in his description of Athyris Maia, nor have I suc- 
ceeded in detecting either a hinge-area ora fissure in any of the specimens which have come 
under my own notice. I am disposed to believe, therefore, that the Spirifera Maia of Hall is 
distinct from the present species, a view which is further borne out by the apparently much 
greater dimensions of the latter; though on this point I can only judge by Professor Hall’s 
figures, and by his statement that the shell of Spirifera Maia is “below the medium generic 
size,” which is certainly not true of Athyris Maia. At the same time, in the absence of any 
definite knowledge of the internal characters of Athyris Maia, beyond the general statement, 
by Mr. Billings, that its internal structure resembles that of 4. naswta, (=A. clara), it is per- 
_ haps hardly safe to assert positively that it belongs to the genus Athyris. 
Locality and Formation.—Corniferous Limestone of St. Mary’s (Collected by Mr. Hinde). 
