OF CONCHOLOGY. 



133 



OBSERVATIONS ON MELANTHO 



BY JAMES LEWIS, M. D. 



A. number of years ago my attention was first invited to the 

 embryonic young of those species of Viviparidae now comprised 

 in the subgenus Melantho, by the contrasts in color exhibited by 

 the young of M. rufa, Hald., when compared with the young of 

 other species associated with rufa in the same station. The dif- 

 ferences then observed still continue to excite my interest, and 

 stimulate me to seek other differences in specimens from distant 

 regions. My investigations relative to the embryonic young of 

 various species of Melantlio are gradually leading me to the con- 

 viction that, in many instances in which the external characters 

 of species are not decided enough to claim attention, it will be 

 found that the embryonic young afford suggestive differences, 

 which can safely be regarded as specific tests. The differences 

 thus far observed in the embryonic young of various species of 

 Melantlio may be expressed as follows : 



Color. — There does not seem to be so great diversity of color 

 as of other conditions. Mention may be made of the pink tint 

 of the young of rufa, the pale greenish tint of the young of de- 

 cisa, the light horn color of all other species yet examined in 

 which the differences in color are scarcely sufficient to arrest 

 attention. 



Form. — -The variations in form are only in a few instances 

 very remarkable, and relate principally to those arrangements of 

 the whorls which, when varied, may produce globular or conical 

 forms. 



Size. — The differences in size seem to be inversely as the num- 

 ber of specimens contained within the gestatorial sack of the 

 parent. 



Number. — The number of specimens contained within the pa- 

 rent (as determined by averages) seems to vary in a very re- 

 markable manner ; some species being much more prolific than 

 others, and, what seems a contradictory feature, the fecundity of 

 a species does not agree with the very natural a priori opinion 



