45 



MoDiOLOPSis Nais. (N. sp.) 



Fig. 46. Fig. 47. 



Fig. 46. — Modiolopsis Maia. a, right valve ; b, hinge line. 

 47. — M. Nais. a, right valve ; b, hinge line. 



Description. — Shell, small, oblong, dorsal and ventral margins straight 

 and nearly parallel, posterior extremity slightly wider than the anterior? 

 obHquely and rather abruptly truncated with a moderate curvatui'e. 

 Anterior margin sloping from the umbones at an angle of about 130° ; ante- 

 rior extremity about i the whole transverse length, narrowly rounded and 

 situated just below the middle. Umbones small, slightly flattened by the 

 nearly obsolete byssal sinus ; beaks small, closely incurved but not in con- 

 tact. The valves are moderately ventricose and the umbonial ridge 

 scarcely prominent, the slope from it to the dorsal margin even, gently 

 convex with a barely perceptible concavity just at the posterior dorsal 

 angle. 



Surface with rather strong sublamellose concentric ridges of growth, 

 with finer ones between. 



Transverse length 5 lines ; umbones to ventral margin 2 J lines ; slightly 

 more extended posteriorly ; depth of both valves 2 lines. 



Locality and Formation. — Paquette Rapids, on the Ottawa River. 

 Black River limestone. 



Collector. — Sir W. E. Lo£]:an. 



Modiolopsis Adrabtia. (N. sp.) 



Description. — Sub-triangular, 2 or 3 inches in transverse length, gra- 

 dually tapering from the umbones to the posterior extremity, wliich is 

 pointed or narrowly rounded. Ventral margin straight, gradually curved 

 upwards at both extremities ; anterior margin somewhat straight, descend- 

 ing with an oblique slope below the middle to the narrowly rounded ante- 

 rior extremity, forming an angle of between 60° and 70*^ with the ventral 

 margin. Umbones inconspicuous, somewhat flattened ; beaks small, closely 

 incurved ; valves only moderately ventricose, usually rather compressed. 

 Surface with numerous rounded concentric undulations, two or three in one 

 line. 



