76 THE NAUTILUS. 



rior margin rather short, rather strongly curved ; inferior well 

 curved, more so in front than behind ; posterior margin distinctly 

 truncated, with a well marked angle where joining the superior, and 

 a less marked, rounded angle where joining the inferior margin ; 

 anterior end forming a slight but distinct angle situated rather high 

 up. Surface very finely, irregularly striated, polished ; whitish or 

 straw colored, often leaden-grayish on the beaks, or even all over. 

 Shell moderately thick, nacre whitish ; muscular insertions not very 

 distinct; hinge of essentially the same type as that in Pis. abditum. 



Long. 4-0, alt. 3'4, diam. 2'4 mill. ; 4'7 : 4'0 :2'9 mill, from another 

 place. 



Pis. politum is rather variable in size, and more so in color as 

 noted above, but so markedly constant in its several habitats that a 

 number of different local forms, or varieties could be described. It 

 has some resemblance with Pi's, abditum Hald. and Pis. rariabile 

 Pr. ; from the former it is different by its being somewhat smaller, 

 comparatively shorter and higher, the beaks being less full, the 

 surface finer striated and more polished ; from the latter it is distin- 

 guished by its smaller size, the beaks being less full, the antero- 

 superior margin less straight, and the angle at the anterior end being 

 situated higher up; the shell is thinner and the hinge less strong, 

 the coloration different. With all these differences appearing only 

 gradual, our Plsidium is a good species beyond a doubt and will 

 always be recognized. 



It was found, in May a. c., in the outlet of a small peaty swamp 

 near New Philadelphia, Ohio, about 200 specimens, in company with 

 Pis. abditum, varibile and compressiim, all, when fresh, being of a 

 remarkably uniform color and appearance; Philadelphia, Pa. 

 (Morris Schick) ; Grand Rapids, Mich. (L. H. Streng) ; Joliet, 111. 

 (Jas. H. Ferriss); Clearwater River, and Dallas Lake, Minn. (H. E. 

 Sargent). 



P. MILIUM Held. This is not a new species, but new to our 

 country. A number of specimens from East Twin Lake, at Charle- 

 voix, Michigan, dead shells but in perfect condition, in the collection 

 of Mr. Bryant Walker, were, after careful comparison, found to be 

 congruent, in shape and appearance, as well as in the hinge char- 

 acters, with one of the larger forms of Pis. milium from England, so 

 that there can be no doubt in their identity. 



New Philadelphia, Ohio, Oct., 1895. 



