THE NAUTILUS. 135 



-ungulata I believe that species to be its nearest ally ; the two forming 

 a group peculiar to the Pacific drainage of the United States, and 

 quite distinct from Anodonta ivahlametensis, calif or niensis, nuttalli, 

 oregonensis, kennerlyi, and youkonensis, which undoubtedly group with 

 Anodonta cygnea, and which may have descended from that protean 

 species, and reached North America by way of a former land pass- 

 age in the neighborhood of Bering Strait. A dorsal view reveals 

 a striking resemblance between the present species and Anodonta 

 angidata ; both have the area of greatest inflation about one-third 

 the length of the shell from the posterior point, from which they 

 gradually narrow to near the anterior end, where they become more 

 rapidly compressed to the point, the beak sculpture is similar ; the 

 general outline of the shells is much alike, and there is quite a strong 

 resemblance in the texture and the nacre. Anodonta angidata in 

 the Museum collection (Mus. no. 104,165) from Northern Calfornia, 

 shows a remarkable fading out of the peculiar keel common to that 

 species, and another specimen (no. 104,166) from Los Angeles shows 

 still less of this character, and in a photograph taken by Mr. Hemp- 

 hill from a specimen in his collection it is wanting altogether, while 

 the two sulcations on the posterior slope show quite plainly. 



At the same time, the species under consideration difiers sufficiently 

 from Anodonta angulata in texture, and the form of the inflation of 

 the posterior region in the female to separate it at once specifically 

 from that form.' This new species will be figured when the large 

 amount of land and fresh-water material from the western United 

 -States collected by the Biological Survey of the Agricultural 

 Department is worked out, and the results published. 



THE SHELL-BEARING MOLLTISCA OF MICHIGAN. 



BY BRYANT WALKER, DETROIT, MICH. 



Aplexa sp. A small species about the size of Lea's Physa hor- 

 dacea and apparently related to it, was found in a small lake lying 

 between Torch Lake and Grand Traverse Bay in Antrim County. 



' So far as I know no description of the soft parts of Anodonta angu- 

 lata has ever been published. 



^ The following portion of Mr. Walker's paper should have api^eared 

 in the August Nautilus. 



