66 



The beak of the ventral valve is small, prominent, and slightly incurved ; the area of 

 moderate width, and sometimes with a smooth triangular space occupying the place of the 

 i-ii-dinen. The dorsal area narrow. 



The surface is marked with " numerous crowded striae, about nine or ten of which are 

 ii;uch stronger and m6re elevated on the umbo of the ventral valve, with finer ones coming in 

 between and on either side; striae frequently increasing by intercalation and bifurcation, until 

 they become very numerous and much finer at the margin. On the dorsal valve, the striae 

 are similar to those of the ventral valve " (Flail). 



According to the observer just quoted, " the interior of the ventral valve, and casts of 

 the same, show a large flabelliform divaricator muscular impression, which is somewhat widely 

 separated in front, and each division distinctly lobed. The occlusor muscular impressions 

 occupy a semi-elliptical space on each side of a narrow central depression, the marking on 

 either side being double in well preserved specimens. The upper extremities of this im- 

 pression are close under the arch of the umbo, and separated by a smooth space from the 

 divaricator impressions. Beyond the muscular impressions, the interior surface is minutely 

 pustulose, the points being more prominent just without their limits ; beyond which the 

 course of the vascular impressions can be distinctly traced. In the dorsal valve the anterior 

 and posterior occlusor muscular impressions are very conspicuous and deeply marked, and 

 often limited by an elevated ridge, a narrow longitudinal ridge dividing the two pairs. On 

 each side, and below the muscular impressions, the surface is marked by small pustules or 

 tubercles ; and beyond these the surface is minutely pustulose, the vascular impressions be- 

 coming distinct towards the margin. The cardinal process is divided from the base, the 

 divisions strongly diverging." (Puloeontologg of New York, Vol. IV, p. 103. 



S. demissa, like the preceding, belongs to the section elevated by Hall to the rank of 

 a genus under the name of Strophodonta. It is a variable species, and unless the hinge-line 

 be preserved with the area, it is not alvvys possible to refer examples to it with certainty. 

 The species occurs in almost every sub-division of the Devonian series of North America. 



Locality and Formation . Corniferous Limestone of Port Colborne and of numerous other 

 localities in Western Ontario. 



78. STROPHOMENA INEQUISTRIATA (Conrad). 



Strophomena mequistriata (Conrad), Journal Acad. Nat. Sciences, Philadelphia, Vol. 

 VIII., p. 254, Plate XIV. Fig. 2. 



Stiopliomena inequistriata (Hall), Geol. Rep. 4th District, p. 200, Fig. 4; and Tenth 

 Beport on the State Cabinet, p. 142. 



Strophomena inequistriata (Billings), Journal Canadian Institute, New Series, Vol. VI., 

 p. 338. 



Strophodonta inequistriata (Hall), Pal. New York, Vol. IV., p. 106, Plate XVIII, Figs. 

 2aL 



[Compare Ortlus inter strialis (Phillips), Pal. Foss. p. 61, Plate XXV. Figs. 103 a-d; 

 Leptcena inte/- strialis (Davidson), Brit. Fossil Brachiopoda, p. 85, Plate XVIII., Figs. 15-18 ; 

 Strophodonta varistriata, var. arata (Hall), i'al. New York, Vol. III., p. 183, Plate 18, Figs, 

 la-*'; Stnphodmta textilis (Hall), Pal. New York, Vol. IV., p. 108, Plate XVIII. Fig. 3; 

 and Strophodonta concava (Hall), Pal. New York, Vol. IV., p. 96, Plate XVI.] 



Shell semi-oval or semi circular, widest at the hineje-line, which varies from one to three 

 inches in length. Cardinal angles usually somewhat acute, and sometimes eared. Width of 

 the shell usually from a fourth to a third greater than the length. Valves concavo-convex ; 

 the ventral valve convex, with a variable curvature, often abruptly arched towards the margin ; 

 the dorsal valve concave, but generally less slrongly curved than the ventral. Beak of the 

 ventral valve apparently very variable in its prominence ; the area narrow, vertically striated, 

 and crenulated in the neighbourhood of the beak. 



i*urface marked with distant elevated simple striae, which increase towards the margins 

 of the shell by interstitial additions, and which are separated by flat or slightly concave inter- 

 spaces, distant from half a line to a line at the margin. These interspaces are occupied by 

 exceedingly fine and close longitudinal striae, from four to ei-zht existing in one interspace. 

 Further, the coarse and fine radiating striae are cancellated by a crowded series of exceedingly 

 fine and cl se-set concentric striae. 



