182 



Dimensions of an average specimen, the original of fig. 1 : maximum 

 length, 5-8 mm. ; height at the midlength, 5 -2 mm. 



Inmost or Birch Island, Kinwow Bay, Lake Winnipeg, where a few 

 specimens were collected by Mr. Weston in 1884 and by Messrs. Dowling 

 and Lambe in 1890. 



A cast of the interior of the left valve of a shell which is probably 

 referable to this species, in a loose piece of limestone, was collected by 

 Mr. Dowling in 1890, at Reindeer Island, Lake Winnipeg. This speci- 

 men, which is represented by fig. 3, on plate 20, is much larger than the 

 specimens from Inmost Island, much more produced at the base posterior- 

 ly, and has a comparatively shorter posterior wing. 



Byssonychia intermedia, Meek and Worthen. (Sp.) 



Ajiibonychiainiermedia, Weeli&ndWoTthen.lSSS. Geol. Surv. 111., vol. Ill, p. 306. 

 Byssonychia intermedia, Ulrieh 1894. Lower Silur. Lamell., Minn, (advance 



copies fr. Geol. Minn., Final Rep., vol. 



III., pt. 2) p. 499, pi. 35, figs. 23-26. 



In the United States National Museum there is a single specimen of 

 the right valve of a shell, which Mr. Ulrieh has recently identified with 

 this species, labelled "Lower Fort Garry, Charles L. Anderson, No. 

 5214." 



MoDiOLOPSis PARViusCDLA, Billings. 



Modiolopsis parviuscula, Billings 1859. In Hind's Rep. Assinib. and Saskatch. 



Bxpl. Exped., p. 186. 



"This species closely resembles M. modiolaris (Conrad) but is always 

 much smaller. It is transversely elongate, anterior extremity small, 

 rounded, half the width of the posterior ; the latter obliquely truncate 

 and spmewhat straight from the end of the hinge line for rather more 

 than half the width, then rounded at the lower posterior angle. Hinge 

 line straight or a little arched, full three-fourths the whole length of the 

 shell. The umbones are less than one-fifth the length from the anterior 

 extremity. The valves are moderately convex, obscurely and obliquely 

 carinate from the umbones towards the lower posterior angle. In many 

 specimens the ventral margin is concave near the anterior extremity, as 

 if for the purpose of a byssus. Surface with obscure concentric undula- 

 tions of growth. Length of large specimen, one and a half inch. In 

 general Jhey are a good deal .smaller." 



" This shell so much resembles M. modiolaris that I have long hesi- 

 tated as to the propriety of giving it a separate name. It is very widely 

 distributed, since we have specimens from Lake Winnipeg at Punk 

 Island, from the Pallideau Islands in Lake Huron, where it occurs in 



