183 



strata -which hold fossils of the Chazy, Black River and Trenton lime- 

 stones, and from near Cornwall and the Island of Montreal in the 

 Chazy." — E. Billings (op. cit.). 



In the Museum of the Survey there are three specimens of M. parvius. 

 aula which are labelled as having been collected by Professor H. Y- 

 Hind at Punk Island in 185S, but, although from the typical locality, 

 they are all so imperfect and so badly preserved that their characters 

 are indefinite and their specific relations obscure. It has been found 

 impracticable to make a satisfactory drawing of either of these speci- 

 mens, as their original outlines are not sufiiciently distinct, and the 

 writer has seen no others from the Lake Winnipeg region. 



MODIOLOPSIS ANGUSTIFRONS. (N. Sp.) 

 Plate 20, fig. 4. 



Shell moderately elongated, nearly twice as long as high, slightly 

 arcuate, very narrow, in the direction of the height, anteriorly, and 

 expanded in the same direction posteriorly, the greatest height being 

 at a short distance from the posterior end : valves moderately convex, 

 most prominent on the broadly rounded, oblique, posterior umbonal 

 slope, in front of which there is an abrupt concave inflection or shallow 

 constriction. Anterior side very short, narrow in the direction of its 

 breadth or thickness as well as height, and rounded at the end : posterior 

 side much longer than the anterior and rather more than twice as high : 

 posterior end obliquely subtruncate above, rounded and somewhat pro- 

 duced below : ventral margin, or margin of the valves in the byssal 

 region, shallowly concave a little in advance of the midlength : hinge 

 line nearly straight and gently ascending behind the beaks, occupying 

 rather more than one-half of the entire length of each valve : umbones 

 broad, depressed in the middle but tumid behind : beaks depressed, 

 incurved, inclined forward, and placed at a short distance from the 

 anterior end. 



Surface markings unknown, though the well preserved and perfect 

 cast of the interior of both valves upon which the preceding description 

 is based, is marked by numerous small concentric plications, which are 

 most strongly marked on the upper part of the valves and behind the 

 beaks. 



Dimensions of the only specimen collected : greatest length, 47 '5 mm. ; 

 maximum height, 26 '-S mm. : greatest height in front of the beaks, 12 

 mm.; approximate thickness of the two valves when closed, about 16 

 mm. ; length of hinge line behind the beaks, between 28 and 30 mm. 



Lower Port Garry, T. C. Weston, 1884 : a cast of the interior of a 

 specimen with the valves widely open. 



