REPORT OF THE DIRECTOR 1 9 ID 1 83 



backward as they fall to the central part of the valve when they turn 

 gradually forward becoming more and more nearly parallel with the 

 hinge. 



Remarks. This species lacks the sharply raised, evenly spaced, 

 threadlike lines characteristic of the Mississippi valley species. In 

 this respect it resembles the British species, but the posterior margin 

 is truncated at about right angles to the hinge, instead of being very 

 oblique. 



One specimen, the largest, appears to have a radiating ridge nearly 

 parallel to the hinge and just below it, but it is probably the hinge 

 of the slightly displaced opposite valve showing on account of the 

 compression of the specimen. 



Aviculopecten debertianus Dawson 



Aviculopecten debertianus Dawson. Acadian Geology, p. 307, 

 fig. 116, 1878. 



One specimen, hardly half a valve, reproduces almost perfectly 

 the characters of this species. 



Pleurophorus? sp. 



A single poorly preserved specimen, rather short and stout for 

 shells of this genus, seems to possess the characteristic ridge of shell 

 which produced the usual depression in the cast in front of the beak. 



Cast short, convex, elongate-subquadrate ; hinge nearly as long as 

 the shell, straight ; posterior end truncated almost at right angles to 

 the hinge and extending to the ventral margin, which is straight, 

 rounding rather gradually into the sharply curved anterior margin. 

 Umbonal region quite convex, beaks incurved, and placed well for- 

 ward. Umbonal ridge prominent and subangular. 



Dimensions. Length, 10 mm ; height, 6 mm. 



Pelecypoda sp. 

 Three or four species of minute, poorly preserved pelecypods. 



Bucanopsis perelegans White & Whitfield var. minima nov. 



Shells minute, strongly reticulated. Band with a narrow line 

 on either side, and a 

 thin elevated line along the 

 middle. Surface covered 

 with fine, filiform revolv- 

 ing striae, evenly spaced, Bucanopsis perelegans White & Whitfield var. 

 6. -ii- . minima nov. Shells x5; surface x 10. 



or 17 to a milhmeter Oj-ster basin. Coffin I. 



and transverse lines of similar character about 10 to a millimeter, 

 showing a tendency to develop nod€S at the intersections with the 



