MOLLUSCA. 841 



destroyed. The species is a very close ally of the European B. 

 mucronattis Schl., and the two- have frequently been considered 

 as identical. The writer has not had an opportunity to com- 

 pare the New Jersey specimens with a large suite of European 

 examples, but Whitfield states that such a comparison shows 

 the American examples to be, proportionally, somewhat more 

 elongate, and if this be a constant character the American form 

 is doubtless .properly considered as a distinct species. The 

 specimens vary greatly in size and the smaller ones are usually 

 proportionately more slender than the larger ones. It is also 

 frequently the case that at any one locality there is not a great 

 variation in size, an assortment which may be due to the trans- 

 portive power of the water at the time of deposition. 



Formation and locality. — Navesink marl, Atlantic Highlands 

 (108), Middletown (113^), near Crawfords Corner (126'^), 

 near Holmdel (128^, 128^, 127, 194), Marlboro (131), near 

 Freehold (133), near Walnford (148^), Crosswicks Creek (149, 

 147^ 147^, 147*, 195), near Jacobstown (150), near Mount 

 Laurel (166), Mullica Hill (1692). 



• Geographic distribution. — New Jersey, Delaware, North Caro- 

 lina, Alabama, Mississippi, Texas. 



