SCALARI A. 461 



animals ; the spiral operculum, single branchial plume, and 

 almost entire aperture, indicate their relation with the Litto- 

 rinte, whilst the mucous fillets and prominent retractile pro- 

 boscis, the latter a character of the highest value, fix them 

 amongst the immediate points of transition to the Muricida. 



S. CLATHRATULA, Montagu. 

 S. clathratula, Brit. Moll. iii. p. 209, pi. 70. f. 3, 4. 



Animal occupying a densely plicated, milk-white, spiral shell 

 of 9-1 1 volutions. The animal nearly throughout is bluish- 

 white, aspersed at the points of the tentacula, on the head and 

 neck, and margins of the foot, with blotches and spots of 

 snow-white matter. Mantle fleshy, reflexed on the peripheral 

 rib of the aperture, and forming also a short, lax, branchial 

 fold to correspond with the incipient canal of the shell. The 

 head, though very short, is distinct, compressed and crescent- 

 shaped, as in Murex; beneath slightly emarginate in the 

 centre, at which point is the mouth, which is partially, trans- 

 versely and vertically cloven ; from this a long, strong, fleshy 

 proboscis is exserted, which I have repeatedly seen evolved 

 several times in a minute. The tentacula are moderately 

 long, divergent, subcompressed, with blunt terminations. The 

 eyes are very black, not fixed on offsets, but on scarcely raised 

 eminences or decidedly external semicircular inflations which 

 are integral parts of the bases of the tentacula. The foot can 

 be extended beyond the tentacula; it is nevertheless short, 

 narrow, and bevelled on both sides, arcuated gently in front 

 when on the march, and slightly auricled ; at rest subtruncate ; 

 it is also grooved transversely in front, dividing the sole from 

 the upper part, and forming a distinct labium, the sole being 

 somewhat the longest ; it tapers to a slender, rounded termina- 

 tion, carrying at some distance from the extremity, on a simple 

 lobe, a white, spiral operculum of three turns ; the first two 

 are very small and eccentric, the third rapidly increases and 

 occupies y 9 Q-ths of the area, and is marked with elliptical striae 

 of increment. The posterior half of the foot is deeply grooved 

 longitudinally and medially in the sole with a central depres- 



