60 AMERICAN JOURNAL 



clearly and positively distinct, and which appears to be the con- 

 necting link between the subgenera 3Ielantho and Vivipara. 



Mr. Binney should have made a unit of his system of classifi- 

 cation (for the sake of consistency). He should have been guided 

 by Say's illustration of decisa, and reduced ponderosa to the rank 

 of a synonym, under decisa. This mode of treatment, carried to 

 its full length, would have relieved the subject of all its perplexi- 

 ties, and given us all there is of Melantho in the simplicity of 

 the single species decisa ! 



But we shall not be content with this partial and incomplete 

 method of Mr. B., and, since he has failed to carry it to an ulti- 

 matum, we may question the correctness of a very large portion 

 of his views on Melantho. 31. obesa (the only Melantho for 

 which that name has been suggested) is a good species, as is 

 evident from the embryo to the adult. 



M. Milesii (assigned to decisa by Mr. Binney) has claims to 

 the rank of a species which must be recognized. And, since he 

 has generally made his errors of opinion conspicuous in the sub- 

 genus Melantho, we may sum up the matter by saying that to 

 the best informed investigators of those species, Mr. Binney's 

 opinions are simply so many interrogation points. They are not 

 useless, for they will invite careful investigation. 



Mr. Binney's illustrations of the sexes of " M. decisa, var. 

 Integra" exhibit extreme cases of divergence. Usually the 

 forms of the sexes differ less conspicuously, and not enough to 

 aid in discriminating one from the other. His illustrations and 

 remarks on abnormal, deformed and reversed specimens might 

 have been extended to embrace much very useful and suggestive 

 information which he omits. 



With the subgenus Liojplax Mr. Binney has exhibited the same 

 conservative spirit which is apparent in his treatment of 31elan- 

 tho. He reduces all its species to two, — a procedure which can- 

 not at present receive sanction. Until all the various types 

 which have been named under Lioplax have been fully compared, 

 from the embryo to the adult, the several species must be re- 

 cognized. 



It will be apparent to any one who will carefully consider the 

 differences in form and size that are exhibited by the various 

 shells of Virginia and Pennsylvania on the one hand, and the 

 western States on the other hand, that those called subcarinata 

 probably embrace more than one species. 



The shell which, on page 70, Mr. B. calls ^Bythinella obtusa," 

 may with propriety be doubtfully regarded as a Bytliinella. It 

 has characters entirely distinct from those of the other species 



