15 



P. TRIVOLVIS, VAR. FALLAX. 



Plate 3.— Figs. 1—3. 



P. testa subdiaphana; pagina sinistra carinata, calicifor- 

 mi; calice lato, niinime profundo: anfractibus 4, minute 

 striatis: suturis impressis. 



SYNONYMS AND REFERENCES. 

 P. LENTUS, Say, Gould. Invert, of Mass., p. 202, fig. 132. 



DESCRIPTION. 



Animal dark brown, minutely dotted with 

 ochre-yellow, upon the parts which are usually 

 exposed: tentacles very long, colored like the 

 body, except that the tint is somewhat lighter 

 near the base: foot, posterior to the neck, about 

 equal in length to the head in front of the ten- 

 tacles. 



Shell thin in texture, translucent, and trans- 

 versely striate: two and a half turns are visible 

 above, the remaining ones disappearing in the 

 narrow umbilic: lower side carinated, having a 

 wide, shallow cup, as in figure 9, when the left 

 posterior angle of the aperture advances along 

 the carina; but the symmetry of the cup dis- 



