6 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCIDIFERA. 



B. Rhachiglossa. 



Radula iiormally 1.1.1, seldom without rhachian tooth or wholly atrophied; 

 sometimes accessory plates but without cusps. Snout pleurembolic. 



C. Toxiglossa. 



Radula normally 1.0.1, seldom with rhachian teeth; seldom wholly absent. 

 Snout usually introversible within a tube-like rostrum. 



Synopsis of Genera and Species. 

 Fam. Cypraeidae. 



Trivia Gray 1832. 



Mantle-lobes covering nearly the whole shell (in living state); radida 2.1.1.1.2. 

 Shell transversally ribbed (rarely smooth), columella in its foremost (lower) part 

 concave, ribbed. 



Shell o väte without dorsal impression, white or pinkish with more or less consp- 



icuous brown döts or clouds, ribbed (or sometimes smooth). Mantle orange with lightfer 



papillse, red spöts and blackish stripes; foot påle yellowish brown with lighter margins. 



L. (sh. ) 10 — 13 mm T. arctica [(Solander) Humphrey 1797] 



• (= CyprseaeuropseaMoNTAGU 1808). 



n. 4, Figs. 36—40. 



Fam. Naticidae'. 



I. Operculum calcareous; shell globose, solid, smooth (or finely striated); umbilicus 

 closed by a callus; the median tooth of the radula 3-cuspidate, the laterals with a 

 strong median cusp and 2 — 3 smaller onea on eacli side of it; uncini simple 



Natica Adanson 1757. 



II. Operculum corneous; umbilicus open or partly covered; the inner uncini bicuspidate. 



A. The median tooth of the radula 3-cuspidate; the laterals as in Natica. Shell 



globose, solid, with regularly convex whorls; inner lip slightly curved without 



columellar sinus. 



1. Shell smooth or finely striated with a smooth, shining cuticula and im- 

 pressed simple suture, usually with an open umbilicus; columellar margin 



* 



' The genus Aniaura, Möllei; 1842, formerly rcfcrred to tliis faniily, must l)c i>la(^e(l iu Fam. Pyrami- 

 dullidcC. The foot is dcvoid of metapodium and propodium, characteristic of tlic Naticid;«; instcad of the lalter 

 a bilobed mentum is present; jaws and radula are wholly absent; tlic eyes, according to Möllei; 1842, are pcr- 

 ceptible on the base of the tentacles (»ad basin intcrnam lobi»), and the spirc of the shell is obviously hetero- 

 strophic. (Cfr. Dall & Baktsch 1904.) 



