20 Trans. Acad. Sci. of St. Louis. 



21 weeks. Length 25.00; width 9.00 mill. 

 33 " " 26.50; " 9.50 " 



52 " " 26.00; " 11.50 " 



52 " " 28.50; «• 10.50 " 



Another remarkable set showing development was pre- 

 sented by Dr. Lyon. The tablet contains fifteen specimens 

 which were all killed when seventeen weeks old, yet the 

 smallest is 4 mill, long and the largest 27 mill. All were fed 

 on lettuce and contained in a four quart battery jar, under 

 equal conditions of heat and light, and the brood was from a 

 single egg capsule. 



8a. LlMNAEA REFLEXA ATTENUATA Say. 

 PI. I.j. 4. 



Limnaea attenuate/, Say, New Harm. Diss. 2 : 244. 1829. 

 Limnata subulata Dunker, Kiister, Chenm. ed. 2. p. 24. pi. iv. f. 24. 



Shell: With an attenuated spire, which is more pointed 

 than in reflexa; whorls 7, somewhat loosely coiled, leaving a 

 well-marked suture, very convex; apex small, rounded, prom- 

 inent; aperture about a third the length of the entire shell, 

 lunate, thickened on the inside by a heavy callus; peristome 

 thin ; columella covered by a heavy callus and with a prom- 

 inent plait; color light horn, sometimes darker, aperture dark 

 horn, the callus yellowish, bordered with dark brown ; other 

 characters as in reflexa. 



Length 24.00; width 8.00; aperture length 9.50; width 5.25 mill. 

 " 23.00; «' 7.75; " " 9.00; <* 5.00 " 



" 22.00; " 7.00: " " 8.75; " 4.75 " 



Animal, Jaw and Dentition as in reflexa. 



Distribution ; Same as reflexa, with the addition of Mexico. 



Habitat: Same as reflexa. 



Remarks: The present form cannot stand, in the writer's 

 opinion, as a species. It intergrades with forms of reflexa, 

 and cannot be satisfactorily separated from that species. It 

 may, however, stand as a variety, characterized by an attenu- 

 ated spire, rounded whorls and general scalariform shell. 

 The variety is very rare and is only known from the vicinity 

 of Joliet. 



