186 THE CHICAGO ACADEMY OF SCIENCES. 



TYPE LOCALITY : Bois Blanc Lake, Manitoba. 



ANIMAL : "Blackish, the head and tentacles marked with small 

 yellow spots which give a brownish color on close inspec- 

 tion, and when the animal is in motion the surface has the appearance 

 of being covered with a superficial bloom of a russet color; foot of 

 blackish gray, lighter beneath; mantle bluish gray, slightly tinged with 

 yellow toward the posterior angle of the shell aperture. Head broadly 

 semi-circular, spreading below, obtusely angular at the posterior lateral 

 margins and slightly emarginate in front. Foot disc broadly rounded 

 in front and tapering behind to an obtusely rounded point; about five- 

 eighths of an inch wide near the anterior end, and together with the 

 head measures about one inch and five-eighths in length when the 

 animal is in motion. Tentacles broad and thin, more than half an 

 inch long, slightly curved inward and irregularly tapering to an obtuse 

 point. Eye spots small, situated at the inner base of the tentacles; 

 yellow in color, with a black center. Respiratory orifice of the pul- 

 monary sac situated a little less than half an inch from the posterior 

 angle of the shell aperture, and when dilated, as in the act of receiving 

 air, is about one-fourth of an inch in its greatest diameter, and regu- 

 larly oval in outline." (Whitfield. See plate XXV, figs. 1-2.) 



JAWS (plate VI, fig. E) : Median jaw about three times as wide 

 as high, with a broad convex median projection on the cutting edge; 

 lateral jaws very long, triangular, the cutting edges somewhat irregular. 



RADULA (plate VII, fig. D) : Formula: f j+f +Y-+T+-I -f +tl 

 (48-1-48). Central tooth with a broad, short cutting point; lateral 

 teeth rather short, quadrate, broad, tricuspid, the second to tenth teeth 

 narrow, the entocone placed nearer the distal end of the reflection; 

 several of the lateral teeth show a tendency to a splitting of the meso- 

 cone, a small accessory cusp resulting, as figured by Whitfield ; eleventh 

 to fourteenth laterals becoming narrower toward the marginal teeth, 

 which begin at about the eighteenth tooth, the reflection being narrow, 

 with three or more cusps at or near the distal end and one or more 

 higher upon the outer margin ; outer marginals very narrow, irregularly 

 tri-, quardi- or penta-cuspid. The fifteenth to seventeenth teeth are 

 intermediate, the entocone moving upward and becoming larger; the 

 eighteenth tooth is a typical marginal. 



The radula differs somewhat from Whitfield's figure (Bull. Amer. 

 Mus. N. H., I, pi. v, fig. 10), in which the lateral teeth are wider, 

 with a longer, more acute mesocone. No example of megasoma has 

 been seen with a radula exactly comparable with the figures of the 

 lateral teeth as shown by Whitfield. 



