The Nautilus. 



Vol. IV. rEBRUARY, 1891. No. 10. 



FORMS OF AMERICAN CARYCHIUM. 



KY II. A. PILSBRY. 



The forms of Garyckium found in America have all been referred 

 to the one species exiguwn by jNIr. Binney. In examining a series 

 collected by ]Mr. Geo. W. Dean of Kent, Ohio, referred to me by my 

 friend John Ford, I found a certain form which Mr. Dean con- 

 sidered distinct. It is far more slender than ordinary exiguum. 

 The amount of difference is considerable, and only the extreme 

 minuteness of the shells has prevented conchologists generally from 

 recognizing it. One conchologist however, has done so: — Henry 

 Carey Lea, Apostle of microscopic shells ! The forms may be distin- 

 guished thus : 



C. exiguum Say, (typical). Rather cylindrical, the next to the 

 last whorl nearly equaling the last in diameter; mouth one-third 

 (or more) the length of shell ; outer lip thickened, expanded, some- 

 times obsoletely thickened, scarcely toothed, in the middle. This is 

 by far the most abundant and generally distributed form. 



('. exiguum var. exile PI. C. Lea. INIuch slenderer than the pre- 

 ceding, longer, more distinctly striated ; mouth smaller, less than 

 one-third the total length of shell ; outer lip thickened, often dis- 

 tinctly toothed in the middle. Specimens described are from Kent, 

 Ohio. 



C. exiguum var. occidentalis Pilsbry. Somewhat larger than 

 typical exiguum, distinctly conical, not at all cylindrical, acute ; 

 outer lip expanded, thin, not at all toothed. It is fz'om Portland, 

 Oregon. 



