GASTEOPODA 



535 



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 : 



a^ Animal pelagic 1. JANTHINIDAE 



a. Animals littoral ,2. SCALABIIDAE 



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 Vmm3 * 



characters of the family: about 4 

 species off the Atlantic and 1 off 

 the Pacific coast. 3 ' foot ; 4 ' floa * > 5 ' ^ gs ' 



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. SCALAEIIDAE. 



2, lateral ; 3, marginals. 



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. grcenlandica 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 (Fig. 829) . Shell long and tapering; 12 mm. 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. 



