22 



Trans. Acad. Sci. of St. Louis. 



ella crossed in the middle by a very heavy plait, which starts 

 from the base of the aperture and runs obliquely into the 

 aperture of the shell about 10 mill, from the junction of 

 the peristome with the body whorl ; there is a spreading 

 callus on the columella and labrum which completely covers 

 the umbilicus. 



aperture length 26.00; width 14.00 mill. (8113.) 



* " 26.50; " 15.00 *' (8113.) 

 ' '« 18.50; " 9.50 ^' (8113.) 



* '• 26.00; '* 12.00 *' (8113.) 

 ^ '' 33.00; ♦* 17.00 '^(Jensen.) 

 ' " 31.00; '^ ' 14.50 " (12315.) 



Animal: Dark horn colored, tinged with bluish on the foot ; 

 head distinct, separated from the body by a constriction or 



neck, and produced into 

 lateral flaps or vela; ten- 

 tacles triangular, rather 

 long, flat, the eyes placed 

 on their bases ; foot short 

 and wide, truncated before 

 and roundly pointed behind, 

 20.00 mill, long and 9.00 

 mill, wide; respiratory ori- 

 fice very large, placed near 

 the junction of the peristome 

 with the body whorl. Heart situated midway between upper 

 and lower ends of columella, pulsations varying from 37 to 

 48 per minute. 

 Jaw: As usual. 



Badida formula : |^ + g^s + ^2^ + i + ^^ + 2^ + U ( ^^— 

 1 — 46) : central tooth as usual, a single membrane examined 

 had the central tooth abnormal in possessing a denticle on 

 the left side of the reflection (/. 13, c. ) ; lateral teeth with 

 a quadrate base of attachment, the reflection very large, 

 reaching far below the base of attachment, bicuspid, the 

 inner cusp very large, the outer cusp very small (the first 

 lateral has a bifid inner cusp); intermediate teeth very long 

 and narrow, bi- or tricuspid; marginal teeth very long and 

 narrow, four- or more cuspid, the cusps being very blunt 

 and small and extending irregularly along the outer edge of 



Fig. 12. Animal of Limnaea stagnalis 

 Linn6. (Canadian Naturalist. 2: 

 196.) 



