273 



the front margin of the ventral valve, and a corresponding fold in the 

 dorsal. 



Umbo of the ventral valve moderately prominent or produced, its beak 

 slightly incurved ; umbo and beak of the dorsal much less prominent and 

 smaller. 



Surface marked with low, rounded radiating ribs, that are wider than 

 the narrow grooves between them. In the most typical specimens there 

 are four ribs in the sinus of the ventral and eight on each side, with a 

 corresponding number on the dorsal ; but in others there are as many as 

 five or six on the fold of the dorsal, and eleven or possibly twelve on each 

 side. In the sinus of the ventral and on the fold of the dorsal two ribs 

 often coalesce near the front margin, a circumstance which has suggested 

 the foregoing specific name. 



Hinge area and characters of the interior of the valves unknown. 



Dimensions of a typical and perfect ventral valve : maximum height, 

 seven millimetres and a half ; greatest width, six mm. and a half. 



A few specimens, mostly single valves or portions of valves, on a small 

 piece of limestone from an exposure twenty-four miles above the mouth of 

 the river. One of these specimens, however, is apparently a ventral valve 

 of a very small specimen of C. Winiskensis. 



Spirifer, sp. indet. 



From loose pieces of limestone at or near the mouth of the river : a 

 cast of the interior of the ventral valve of a small specimen, not more 

 than eight millimetres in width, of a Spirifer, with a narrow mesial sinus, 



Glassia variabilis, Whiteaves. 



• Plate 26, figs. 3, 4 and 5. 



CHassia variabilis, Whiteaves 1904. Geol. Surv. Canada, Ann. Rep., vol. 



XIV, pt. F, p. 42. 



" Shell very small, strongly compressed and lenticular in outline in 

 transverse section, or moderately convex and varying in marginal outline 

 from nearly circular and sometimes a little wider than long to subovate 

 and a little longer than wide. 



" Ventral valve with the front margin either nearly straight and devoid 

 of sinus, or faintly sinuated, or provided with a rather wide but not 

 distinctly defined, shallowly concave but not very deep, mesial sinus, that 

 extends backward to about the midlength. Umbo of the ventral valve 

 small, narrow and not very prominent or produced, its beak slightly 

 incurved and apparently perforate. 



" Dorsal valve with the umbo and beak smaller than those of the 

 ventral. 



