88 



Corniferous Limestone, and present a very characteristic appearance. The unibonal 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 b lunded later- 

 ally by the deep fissures left by the dental larnellse. 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 slope is conspicuously striated with longitudinal striae, 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- 



/ \ zt^r ently bend downwards from near their 



origin ; thence recurving, they follow very 

 a closely the contour of the dorsal valve, 



making thirteen or more turns in an indivi- 

 dual of medium size. Spires, slender and 



a. Cast of the interior of the ventral valve of 4Ai/m aMa, : mr .i /Un]] p f ,J ; \V>/- V>-7" Vnl TV 

 (Conrad), from the Corniferous Limestone (Original) ; b, Interior of Simple ^tiail. r&l, l\6tt IOTK, V 01., J. V ., 

 the ventral valve of the same (after Billings). p 301). 



Locality and Formation. Common in the Corniferous Limestone of Port Colborne and 

 Hagersville. 



106. ATHYRIS(?) MAIA (Billings). 



Athyris Maia (Billings), Canadian Journal, New Series, Vol. V., p. 276, Figs. 33, 34. 



(?) Spin/era Maia (Hall), Pal. New York, Vol. IV., Plate XLIII., 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 striae. 



According to Billigs, 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 (loc. 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 or a 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 A. nasuta, (=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). 



