298 GASTROPODA. [Pectinibmnchia. 



These molluscs are carnivorous ; they secrete a purple fluid, which 

 is ejected from the branchial cavity when irritated. Some species are 

 viviparous. The float can be detached spontaneously. 



Genus 1. JANTHINA (Bolten), Lamarck. 1799. 



Janthina, Bolten, Mus. Bolten. (2), 1798, 75 ; Lamarck, Prodrome, 1799. 

 75. Type : Helix janthina, L. 



Head large, muzzle-shaped ; tentacles forked, so that each appears 

 like a pair ; foot rather short, the epipodial lobe somewhat elongated 

 and ciliated ; branchial plumes 2, unequal. The radula is composed 

 of a great number of elongated teeth ; there is no central tooth. 



The float is found in both sexes, and, whilst in the female the eggs 

 are usually attached to the lower surface thereof, the animal in some 

 species is viviparous ; embryos taken from the uterus are operculated ; 

 the head has a ciliated velum ; the eyes are large and well pigrnented. 



Shell imperforate. without epidermis, fragile, trochiform or turbini- 

 form ; nucleus small, styliform, oblique ; spire light purplish-white, 

 base deeper purple ; whorls few. convex, with strife of growth, angular 

 or gathered at the periphery ; outer lip with a sinus in the middle ; 

 columella thin, twisted. 



About thirty species have been described from the Atlantic and 

 Pacific Oceans, which Tryon reduced to three species and a few 

 varieties. 



A species is found in the Pliocene of Italy. 



Vernacular Name. Violet snail. 



KEY TO SPECIES. 



A. Periphery subangled ; sinus not very deep, rounded. 



a. The whole of the base violet, spire elevated . . . . communis. 



aa. A white band round the columella, spire depressed . . balteata. 



B. Periphery rounded ; sinus deep, sharply angular. 



a. Shell plicately radially striated, polished . . . . . . globosa. 



aa. Shell sharply radially striated, not polished . . . . exigua. 



1. Janthina balteata, Reeve, 1858. Plate 44, fig. 10. 



Janthina balteata, Reeve, Conch. Icon., xi, 1858, pi. 3, f. 11 ; Thes. Conch., 

 v, 1882, 50, pi. 443, f. 12 ; Man. Conch. (1), ix, 3<>, pi. 9, f. 1)8. J. fragili*, 

 var. planospirata, Ad. & Rve., Index, 80 ; not of Adams and Reeve. 



Shell depressed globose, thin, with narrowly convex periphery. 

 Sculpture consisting of oblique growth-striae, sinuated at the periphery ; 

 crossed by inequidistant spiral lines, cut up by the radiate stria?, more 

 conspicuous upon the base. Colour : Violet-white above, blue or violet 

 beneath, with a conspicuous white band round the columella, which 

 is very dark violet. Spire depressed conoidai, about one - third 

 the height of the aperture ; outlines convex. Protoconch minute, 

 pupiform, oblique, of 3 smooth whorls. Whorls 6, slantingly convex ; 

 base flatly convex. Suture impressed. Aperture, transversely oval, 



