GASTROPODA 



535 



Fig. 828 — Janthina fragilis (Cambridge 

 Natural History). 1, gill; 2, tentacles; 

 3, foot ; 4, float ; 5, eggs. 



Division 1. PTENOGLOSSA. 



Shell conical or discoid, with a small, simple aperture; no siphonal 

 canal; radula with or without central tooth, but with numerous small 

 laterals: 3 families, all marine. 



Key to the families of Ptenoglossa here described: 



Oi Animal pelagic 1. Janthinidae 



Oj Animals littoral 2. Scalariidae 



Family 1. JANTHINIDAE. 



Shell thin and transparent, heliciform; 2 free ctenidia; foot small, 

 secreting a long vesicular float, which supports the animal at the surface 

 of the water, and to which the eggs are attached ; when handled, the animal 

 exudes a violet fluid: 12 species, in 

 warm waters, pelagic, gregarious, 

 feeding largely on jellyfish. 



Janthina Lamarck. With the 

 characters of the family: about 4 

 species off the Atlantic and 1 off 

 the Pacific coast. 



J. fragilis Lam. (Fig. 828). Shell 20 mm. high; diameter 25 mm.; 

 color violet : tropical and pelagic, sometimes thrown up on the shores of 

 New England. 



Family 2. SCALAKIIDAE. 



Spiral staircases. Wentletraps. 

 Shell an elongated cone, white, with 

 many very convex whorls, which are 

 crossed by elevated ribs; operculum 

 horny; a short siphon present; the 

 animal exudes a purple fluid: about 4 

 genera and 200 species. 



ScALARiA Lamarck. With the 

 characters of the family: numerous 

 species on the Atlantic coast, mostly in deep water and towards the south. 

 S. groBnlandica Perry. Shell rather long and tapering, 25 mm. long 

 and 9 mm. thick; whorls 10; ribs white, on a whitish or brown surface, 

 which has 6 or 8 revolving ridges: Cape Cod to the Arctic Ocean, in 10 

 to 100 fathoms ; often common ; Europe. 



S. lineata Say (Pig. 820). Shell long and tapering; 12 nun. long and 5 



mm. thick; whorls 11: Cape Cod to Florida; common towards the south. 



S. angulata Say. Shell 20 mm. long, 8 mm. wide; whorls 6 to 11, 



touching one another only by the ribs: Long Island Sound to Texas, 



common towards the south. 



Fig. 829 Fig. 830 



Fig. 829— Scala lineata (Verrill). 

 Fig. 830 — Radula of Vermetus (Cam- 

 bridge Natural History). 1, central; 

 2, lateral ; 3, marginal's. 



