216 RETUSA. 



is rarely mamillate or scalariform. This form is common in the 

 Mediterranean. Alt. 1-1 4, diam. ^-f mill. 



R. PERTENUIS Mighels. PI. 23, figs. 48, 49. 



Shell small, thin, translucent whitish or light brown, cylindrical, 

 the spire very low-convex ; whorls 3?, the first somewhat turned in- 

 ward ; sutures deeply impressed ; last whorl descending, sculptured 

 with irregular, light, arcuate growth-striae. Aperture narrow above, 

 dilated below ; outer lip strongly arched forward and bent slightly 

 inward in the middle ; columella thickened but not plicate. 



Alt. 3'2, diam. 1-8 mill. 



Massachusetts Bay ; Fernandina, Fla. ; Coast of Maine ; Green- 

 land', Norway. 



Bulla pertenuis MIGHELS, Bost. Journ. Nat. Hist, ii, p. 346, pi. 

 16, f. 3 Utriculus pertenuis GOULD (W. G. B. edit.) p. 218, fig. 509. 

 SARS, Moll. Reg. Arct. Norv. p. 287, pi. 17, f. 19. AD., Thes. 

 Conch, ii, p. 371, pi. 120, f. 19. Sows., Conch. Icon. f. 4. BALL, 

 Blake Gastr., p. 45 ; Cat. Mar. Moll. S.-E. U. S., p. 86. AURIVIL- 

 LIUS, Vega-Exped. Vetenskap. Arbeten iv, p. 371. D lap hana per- 

 tenuis VERRILL, Amer. Journ. Sci. (3), xx, p. 399. 



This species has been united with R. obtusa and R. semen by many 

 authors, but the three are here retained distinct because proof of 

 their complete intergradation is still lacking. R. obtusa seems to 

 be a more solid, larger shell, replacing pertenuis in English and 

 southern European waters ; B. semen is a somewhat shorter form 

 from high latitudes. 



R. SEMEN Reeve. PL 23, figs. 55, 56, 57. 



Shell cylindrical-ovate, rather tumid, the spire depressed convex, 

 suture impressed ; whorls smooth, slightly convex, the last a little 

 descending in front ; tawny-white. Of a short cylindrical form, 

 somewhat swollen, with a depressly convex spire, having the suture 

 faintly channelled. (Rve.~). 



Port Refuge ; Nova Zemblia. 



Alt. 6, diam. 3.] mill. (Leche). 



Alt. 4i, diam. 3 mill. (Leclie}. 



Bulla semen RVE., in Belcher's Last of the Arctic Voyages, ii, p. 

 393, pi. 32, f. 4a-c, 1855. Utriculus semen LECHE, Kongl. Sv. 

 Akad. Handlingar, xvi, no. 2, p. 71, 1878, (with v. elongata). 



Leche describes a form with higher spire as Var. elotigata. It 

 is not the same as R. turrita Moll. 



