NATURAL SCIENCES OP PHILADELPHIA. 337 



Length 1.33 inches = 34 mm. Greatest width 0.95 inches = 24 

 mm. These dimensions are subject to variation of an exti'erae 

 character. 



Ohio Canal, Columbus, Ohio. H. M. Moores. (Fig. 5.) 



Michigan. 0. M. Dorman. (Fig. 6.) 



In treating Melantho, there seems to have been numerous 

 instances in which species have been misunderstood. M. obesas 

 has been confounded with shells occurring in New York with 

 which apparently it has only very remote relations. 



In my most recent examinations of Melantho, as it occurs in a 

 limited portion of the Erie Canal, near Mohawk, N. Y., I detect 

 three species associated, each constant in its characters without 

 manifesting any tendency to hybridism. A fourth species may 

 possibly be inferred from a division of the various forms I have 

 hitherto regarded as varieties of integer. 



To make this clear to the reader, I have thought proper to offer 

 a series of figures illustrating the characteristics by which I have 

 made a division. 



The prevailing form is illustrated by Fig. 1 of this series. It 

 represents a shell, the whorls of which are very regularly rounded 

 without an}*- tendency to assume gibbous forms. The opercle of 

 the adult shells of this form is very transverse and narrow, resem- 

 bling that of the typical ponderosus of the Ohio River. The 

 texture of the shell is less solid than the gibbous forms exhibit, 

 and the epidei'mis is much paler. The form of Melantho is here 

 illustrated by a specimen more slender in its proportion than a 

 tj^pical shell should be. 



The gibbous forms, as may be inferred from what has been 

 written above, are more solid in their texture and have a darker 

 epidermis. They are usually also more regularly smooth, though 

 gibbous. I have selected three examples as illustrations of the 

 features this form of Melantho displays. Fig. 2 may be regarded 

 as approximating the least gibbous phase, and would probably be 

 regarded as one of the shouldered specimens of which DeKay 

 wrote. Fig. 3 is a form which W. G. Binney confounds with obesus, 

 from which it is sufficiently distinct not to require further notice 

 at this time. Fig. 4 is an extreme form in which the aberrant 

 tendencies of this race of mollusks has been exaggerated by 

 abnormal conditions. These and many other forms in my collec- 

 tion, all part of one series, go far to show that it is unsafe to 

 attempt to decide the limits of species from a few specimens. 



