THE NAUTILUS. 43 



Distinguished by its inflated form, shoulder, low spire, unim- 

 pressed sutures and twisted coluniella. 



Physa vinosa Gould. This variety differs from the type only in 

 having a more globose form, the spire a little more elevated, and im- 

 pressed sutures. 



Physa magnalacustris Walker. This form has been recently dis- 

 covered by Mr. Bryan Walker in northern Michigan. As his des- 

 cription has been published in the NAUTILUS it is not necessary for 

 me to give it here. It is a large, fine globose shell, remarkable for 

 the broad, white longitudinal bands on the last whorl. If they are 

 all like the specimens shown me, it should rank as a species. 



Pliysa crassa Walker. This variety has also been recently de- 

 scribed from forms found in Michigan. It is much heavier and 

 somewhat narrower than the type. It has been well described by 

 its author. 



Physa cmcillaria is distributed over the same territory as P. hetero- 

 stropha Say, but is not so plentiful in the extreme east, and may 

 extend a little further west, but does not cross the Mississippi river. 

 P. obesa, De Kay, is a form of this species. 



Physa sayi Tappan. 



There has been a great deal of contention over thio species. Some 

 of our ablest conchologists contend that it should not rank as a spe- 

 cieSj while others equally as experienced accord it that rank. After 

 having given it much investigation and study, I have decided to re- 

 cognize it as a species. That it is an offshoot of P. anciUaria Say, 

 as that shell is of P. heterostropha Say, I have no doubt ; but has it 

 not by its constant variation from its ancestor established the right 

 to rank as a species? It is not only possible, but highly probable 

 that all the American species of this genus sprung from one form. 

 The evolution began away back in the dreamy past, and has contin- 

 ued in some degree to the present time. When in our investigations 

 we find a form that has maintained distinctive characters for a long 

 period of time -in fact so long that the knowledge of man runs not 

 to the contrary -we must admit it to specific rank. 



It was described sixty years ago from forms taken in Lake Pipin, 

 Portage Co., Ohio, and typical forms are still found having the same 

 inflated form, expanded lip, elevated spire with dark brown apex, 

 five whorls, coarse lines of growth and two varicose bands. 



It is distributed over the northern part of the United States, and 



