390 HYDATINA. 



Radula apparently lacking central teeth, the laterals all of the 

 same form, stout thorn-shaped, the cusps not denticulate. 



In the single species composing this group, the spiral basal funi- 

 cle which is crescentic in Hydutina 'physis, is straightened and 

 pressed against the columellar lip, and its termination below causes 

 a distinct basal spout, which is only slightly indicated in the Hyda- 

 tina. These differences seem, however, quite insufficient for generic 

 separation. 



H. AMPLU8TRE Linne. PI. 44, figs. 1, 2, 3, 4, 5, 6. 



Shell obovate, thin, wider above, tapering below ; the spire wide, 

 convex ; whorls about 5, the first a minute uptilted, partly immersed 

 nucleus, the following whorls planorboid with impressed suture, the 

 last whorl slowly descending, wide above, tapering below. Under 

 a strong brown epidermis it is crimson or pink, with a broad sub- 

 sutural white zone bordered outside by a black band ; a median 

 white zone bordered above and below by black bands (rarely coal- 

 ascent across it), and a white umbilical tract bounded above by a 

 black band. Aperture nearly three times as long as wide, not sin- 

 used above, broadly channelled at base. Outer lip thin, its profile 

 nearly straight, retracted at base. Columella a large subvertical 

 pillar, truncated at base, its inner edge covered with a thin, non- 

 .adherent callus. Alt. 25, diam. 19 mill. 



Bramble Cay, outer Great Barrier Reef, Northeastern Australia; 

 Aneiteum, New Hebrides, New Caledonia (Brazier) ; Upolu, Raro- 

 ionga (Garrett) ; Sandwich Is. (Newcomb, Townsend et al.) ; He- 

 union (Desh., et al.) ; Mauritius (Lienard, et al.) ; and I. Fouquets 

 ((Mobius) ; Mahe, Seychelles (Dufo). 



Bulla amplustre Linne, Syst. Nat. x, p. 727 ; xii, p. 1184. — Han- 

 ley, Ipsa L. Conch., p. 206. — Wood, Index Testae, pi. 18, f. 26, — 

 Bulla ampludra Gmel., p. 3426. — Bulla aplustre Lam., Anim. s. 

 Vert., vi, pt. 2, p. 35. — Quoy & Gaim,, Voy. Astrol., ii, p. 366, pi. 

 26, f. 4-7 (living animal). — Eydoux & Souley'et, Voy. de la 

 Bonite, pi. 25, f. 14-17 (living animal). — Aplustrum amplustre L., 

 MoRCH, Catal. Yoldi, p. 137.— H. & A. Ad., Gen. Rec. Moll., ii, p. 

 7, pi. 56, f. 3.— Chenu, Manuel, i, p. 286, f. 2905.— Hydatina 

 aplustre Martens, Mobius' Reise nach Mauritius, p. 304 ; Donum 

 Bism., p. 51. — Aplustrum fasciatum Schum., Essai, etc., p. 208, 

 {\Sn).—Aplustra pulchella Swains. Malacol., p. 248, (1840).— 

 Amplustre thalassiarchi Martini, Naturlexicon, i, p. 383, pi. 18, f. 



