THE NATURAL HISTORY SURVEY. 235 



Length, 2.50; diameter, 1.30; aperture long, 1.00 mill. (10239.) 

 3.00; " 1.50; " " 1.10 " (10646.) 



2.50; " 1.25; " " .90 " (10237.) 



2.75; " 1.50; " " 1.10 " (11995.) 



Animal: Small, white and transparent, except head, neck 

 and eye-peduncles which are black; foot narrow and long; eye- 

 peduncles long and slender; tentacles conical, short. Respira- 

 tory orifice prominent, placed at the angle of peristome and 

 body whorl. 



Jaw: Long and narrow, slightly arched, the ends a little 

 narrower than the central portion and rounded; convex mar- 

 gin smooth, concave margin notched, and anterior surface ver- 

 tically striated (Fig. 66, J). 



Radula formula: ^l T +l+i+-|+-T ( ! T * n); .central 

 tooth with a base of attachment longer than wide and with the 



Fig. 66. 



Radula of BIFIDARIA CONTRACTA Say. (Original.) c, central tooth; 

 1, first lateral; 7, third marginal; 9, fifth marginal; J, jaw. 



lower outer angles expanded; reflection small, narrow, tricus- 

 pid, the central cusp long, wide, blunt, the side cusps shorter 

 and sharper; lateral teeth with a wide base of attachment, ex- 

 panded on the lower outer angle; reflection narrow, bicuspid, 

 the inner cusp very long and wide, almost reaching the lower 

 margin of the base of attachment, the outer cusp about half 

 as large and sharp-pointed; marginal teeth low, wide, with 

 from three to seven cusps, the single inner being very large 

 and sharp, and the outer cusps short. The fifth marginal has 

 three cusps, the seventh five cusps and the ninth seven cusps; 



