b THE NAUTILUS. 



Me., exhibit a greater or less tendency to develop the transverse pli- 

 cations of this form, but none of them with anything like the strength 

 or regularity of the specimen figured. 



Similar specimens occur in the marl deposits at Bad Axe and 

 other localities in Tuscola Co., Mich. 



It is doubtful whether this form is entitled to rank as a variety. 

 It is evidently an extreme development of the var. striatus, in which 

 the transverse plication has been added to the revolving sculpture. 

 If the name had not already appeared in the literature without 

 description, and required explanation, I should hesitate to describe 

 it as varietally distinct from striatus. 



IV. Var. PERCARINATUS n. n., pL I, fig. 12. 



Planorbis bicarinatus major Walker, Naut. VI, p. 136 (1893); 

 non var. major of various species of various authors. 



Shell very large for the species, thick and solid, dark horn- 

 color tinged with purple ; superior and basal carinae elevated into a 

 distinct keel, which is white; lip thickened, edged with brown, 

 behind which externally is a broad, yellowish-white band, within 

 banded by deep reddish-brown; lines of growth distinct, stronger 

 and '* puckered " around the carinas; revolving lines very faint, not 

 discernible except with a lens; aperture more or less expanded, 

 sometimes distinctly campanulate, auriculate and distinctly modified 

 by the extension of the carinse to the lip. 



The specimen figured measures 18.5 mm. in diameter and 10 mm. 

 in height; height of body whorl in front of aperture 7.25 mm.; height 

 of aperture 10.5 mm. A larger specimen, with a campanulate aper- 

 ture, measures 19.75 mm. in diameter and 10.5 mm. in height. 



Types (Nos. 3419 and 20074, Coll. Walker) from Crystal Lake, 

 Benzie Co., Mich. Also from Pine Lake, Charlevoix Co., Mich. 

 (Walker), and Rideau and Ottawa Rivers; Sparrow Lake, Simcoe 

 Dist., Ontario, and Detroit Lake, Minn. (Pils.). 



The original specimens, collected by the late Dr. M. L. Leach, 

 were all dead shells, more or less bleached. The above description 

 has been prepared from fresh specimens from the same locality col- 

 lected by Dr. R. J. Kirkland, of Grand Rapids. Not in deference, 

 for I think the rule an absurd one, but under the compulsion of the 

 " International Code," I am forced to change the name of this very 

 distinct variety and add another unnecessary synonym to the burden 

 of systematic conchology. 



