31 



Strophomena varsensis, sp. nov. 

 Plate VII, Figure 13 

 Strophomena varsensis, Foerste, MSS. 



In the lowermost 20 feet of the Erindale formation, a brachiopod which 

 resembles Strophomena sulcata, De Verneuil, is so abundant that it is taken as 

 the type species of the zone. 



S. varsensis resembles 5. sulcata in being a moderately convex, rather short 

 shell with a well-defined mesial sulcus in the anterior of the ventral valve and a 

 corresponding elevation in the anterior of the dorsal valve. The Credit River 

 species differs from S. sulcata in its smaller size and coarser radiating plications. 

 The former averages 14 mm. in width and nine millimetres in length, with a 

 convexity of two millimetres, but many specimens are not over 11 mm. in width 

 by seven millimetres in length. The fold and sulcus are scarcely perceptible 

 in these smaller forms, which may represent the immature stages in the life 

 history of the species. The type specimen, somewhat larger than the average, 

 is 16 mm. in width by nine millimetres in length. The radiating plications 

 appear to be much coarser than those of S. sulcata, since in addition to being 

 actually coarser, they are on a considerably smaller shell. They average nine 

 in five millimetres at a distance of five millimetres from the beak, and eight 

 in five millimetres at the anterior margin. The increase in their number is 

 accomplished by fission. 



S. varsensis approaches S. sinuata, James, in the coarseness of the plications, 

 but the latter species is even larger than S. sulcata, while our species is smaller 

 than that form. 



Foerste in a letter to the writer makes the following remarks in reference 

 to S. varsensis: — 



Many of your specimens contain also a coarse ribbed form of Strophomena belonging to 

 the Strophomena sulcata group. The nearest approach to this form in Ohio occurs in the base 

 of the Blanchester division of the Waynesville member of the Richmond formation, where it is 

 associated with Catazyga headi just as in the case also with your Credit River specimens. It so 

 happens, however, that I studied forms of this kind from the Waynesville of the Richmond area 

 east of Ottawa, in Canada, where I called it Strophomena varsensis, in the unpublished manuscript 

 on the fossils of that area. Your specimens resemble the Ottawa Basin specimens more closely 

 than the Ohio and Indiana representatives in having slightly wider radiating plications. 



Locality. — Mullet creek, Erindale. 



No. 12174, Royal Ontario Museum of Paleontology. 



