GASTEROPODA. 107 



Mont. (t. 12, f. 4). The volution of our shell is obtusely but distinctly angulated on 

 the upper part, gi^'ing the suture a deep depression. The specimens are generally 

 more or less rubbed, causing the ribs to appear smooth; but one individual has 

 distinct striae carried over the ribs. I am not acquainted with any recent species with 

 which it can be identified, and have therefore left it with its provisional name. Small 

 shells found in sand, even in a recent state, have their characters sometimes obliterated, 

 from friction by the agitation of the waters ; in addition to which, many species from 

 he Crag, particularly in this genus, have the exterior altered by decomposition or 

 decortication, which renders their identification a matter of great difiiculty. 



12. RissoA suPRA-cosTATA. S. JFood. Tab. XI, fig. 8. 



RissoA STJPRA-cosTATA. S. Wood. Catalogue. 



B. Testa ehngato-conicd, turrifd ; apice parum obfuso; anfractihus 5 — 6, convexis ; 

 mperioribus cosfulatis, et tra7isversim striatis ; anf radii ultimo Icevif/ato ; aperfurd 

 subrotimdd; labro extm incrassato, intus dentimlato ; labia vix reflexo ; umbilico 

 parvo. 



Shell elongato-conical, turreted, thick, and strong, with a somewhat obtuse apex ; 

 volutions 5 — 6, convex, suture deep ; upper whorls longitudinally costated, and 

 transversely striated ; last whorl smooth and tumid ; aperture subcircular, with a 

 continuous peritreme ; outer lip thickened and reflected, with 4 — 6 denticulations 

 within ; and a small but distinct umbilicus. 



Axis, \ of an inch ; diameter, I the length of axis. 



Locality. Cor. Crag, Sutton. 



This is not a very abundant shell in my cabinet, and the specimens are rubbed, 

 their true character being thereby somewhat obscured. It bears a great resemblance 

 to Pj/ramissimilis (Browns Illust. Brit. Conch, pi. 51, f. 20), which M. Loven considers 

 as a var. of membranacea, Adams, Helix labiosa, Mont. As it is at present doubtful 

 I have left it with its provisional name, although probably it may be a known species. 

 The upper whorls are furnished with 10 — 12 rounded and vertical costae, while the lower 

 one is smooth and naked, and it has not the slightest vestige of a thickening or fold 

 upon the columella. Rissoa nana, Grat. (Foss. de Bord.), has the upper volutions 

 costated, but has no umbilicus. 



The names of several of the species in this genus are given as new, while probably 

 they are not so ; being, however, unable to identify them with any known forms, they 

 are left for the present with the provisional names given to them in my Catalogue. 



