342 MALACOZO-A. G ASTEROPOUA . 



This very beautiful, and easily distinguishable shell, is 

 similar in form to Rissoae trvuicata and striata, being oblong, 

 obtuse, of six turns, which are flattened, thick, semitrans- 

 parent, glossy, pure white, witliout stria?, and traversed by 

 strong, closely-set, obtuse ribs, of which there are about twenty 

 on the last turn ; the ribs almost continuous, being but slightly 

 separated by the very small suture ; the aperture rather more 

 than a fourth of the whole length, ovate, narrowed behind, 

 patulous, with the outer lip thick and having an external 

 smooth rim, the inner lip thick, reflexed, le~aving a slight 

 curved groove. Length rather more than two-twelfths of an 

 inch, breadth nearly a third of the length. 



The above description from two fine specimens', found by 

 Mr. Alexander Beaton on Actinias fi-om the Bay of Aber- 

 deen, in February, 1843. 



Tui-bo Bryereus. Mont. Test. Brit. 313. Fl. 15. f. 8.— Chigula 

 Bryerea. Flein. Brit. Anim. 307. 



19. Rissoa suhumhilicdta. Subumbilicated Rissoa. 



Shell ovato-turrite, thick, opaque, the turns six, in- 

 distinctly separated, slightly convex, faintly striate trans- 

 versely, glossy, the last well rounded, the aperture 

 roundish-oval, the inner hp reflexed, leaving an umbilical 

 groove. Subumbilicdtus, somewhat umbihcated. 



Shell ovato-oblong, subturrite, of six thick, opaque, glossy, 

 faintly striated, little-convex turns, indistinctly separated by 

 the suture ; the spire tapering, rather obtuse, shorter than the 

 last turn when viewed on the side of the aperture, which how- 

 ever is little more than a third of the whole length, rovm dish- 

 oval, not acute behind, with the peristome rather thick, re- 

 flexed on the columella, and leaving a distinct umbilical groove ; 

 the colour greyish-white. Length two-twelfths of an inch, 

 breadth nearly half the length. 



This species differs from Rissoa ulvas in not having the 

 aperture acute behind, nor the last turn angulate ; from Rissoa 

 muriatica in being thicker, and from both it and Rissoa ventri- 

 cosa, in having the apertin-e rounded behind. 



Found by me among shell sand, near Don-mouth, in August, 

 1842. 



Tui'bo subumbilicatus. Mont. Test. Brit. 31G. — Cingula sulnim- 

 bilicata. Flem. Brit. Anim. 308. 



