THE NAUTILUS. 141 



erately curved; scutum and scutellum distinct with slight projecting, 

 rounded angles at their terminations, the one at the scutum being 

 less marked in full-grown specimens; anterior and posterior ends 

 almost equally, obliquely truncated, especially in specimens not quite 

 mature, while in the adult the posterior end forms more a regular 

 curve from the beaks down to the rather low-situated rounded end; 

 surface with rather sharp, fine and crowded sulcations, usually some- 

 what coarser on the beaks, dull or with a slight gloss; a few strongly 

 marked lines of growth ; color grayish or whitish-brown in the young, 

 and the same in slightly marked marginal zones of older specimens 

 plumbeous in half grown, and reddish or brownish, or smoky-brown, 

 in the adult, with narrow, darker zones on the lines of growth ; shell 

 thick, muscle insertions distinct, nacre white, almost porcellaneous, 

 with bluish zones corresponding with the lines of growth; hinge 

 strong, plate rather broad, cardinal teeth comparatively large, the 

 right strongly curved, emarginate at the free edge, its posterior part 

 thick, slightly to deeply grooved; the inferior in the left valve short, 

 curved, the superior shorter to longer than the inferior, moderately 

 posterior, oblique, little curved; lateral teeth strong, those of the left 

 valve with very high pointed cusps, ligament rather large, covered. 



Size : long. 15, alt. 11.5, diam. 9.5 mill. 

 Long. 14, alt. 11.5, diam. 9 mill. 



Habitat : Carp Lake, near Mackinaw City, Michigan, collected 

 by Mr. Bryant Walker. 



This is a remarkable Sphaerium. It stands near some large forms 

 of stamineum, yet by its shape, large diameter and very large beaks, 

 is different ; S. solidulum is more rounded in its outlines, less inflated, 

 its beaks are smaller, and the sulcation is coarser. In its surface 

 appearance, sulcation and color, our species resembles S. simile, but 

 is much shorter, comparatively, its beaks are higher, the hinge mar- 

 gin is more curved and the hinge very much stronger. 



Sph&rium walkeri n. sp. Mussel small, well inflated, almost equi- 

 partite ; beaks little anterior, rather broad, rounded, not high, some- 

 what projecting over the hinge margin ; the latter rather short, little 

 curved ; scutum and scutellum scarcely marked, with slight, project- 

 ing rounded angles ; inferior margin slightly curved ; anterior end 

 well rounded, passing into the inferior without any indication of an 

 angle ; posterior slightly truncated obliquely, passing into the inferior 

 with a low situated, rounded angle ; surface with very fine, some- 



