498 MOLLUSCA 



Philine Ascaiiias. Shell with a rudimentary spire, white, translu- 

 cent, oval; animals slug-like; radula wdth no central teeth; foot about 

 two-thirds the length of the body and obliquely truncated : 20 species. 



P. quadrata (Wood). Shell 5 mm. long, 3.5 mm. wide, with 2 to 3 

 whorls, squarely globose: New England north of Cape Cod, in rather 

 deep water; Europe. 



P. lima (Brown). Shell with 3 to 4 whorls, elongate, broadest ante- 

 riorly, 3.5 mm, long, 2 mm. wide, reddish in color: New England north 

 of Cape Cod; Europe. 



Family 6. LIMACINIDAE. (Pteropoda Thecosomata.) 



Shell and mantle present ; shell snail-like, minute, with a left-handed 

 spiral and an operculum ; ctenidium and eyes absent ; 1 pair of tentacles ; 

 mantle cavity, with anus and other openings on right side; 2 large fins 

 present, these being the epipodia, which have extended around the dorsal 

 side of the head : 2 genera and about 19 species, which are pelagic, prin- 

 cipally in the northern seas. 



..""i 



Fig. 759 Fig. 760 Fig. 761 



Fig. 759 — Limacina arctica (Leunis). Fig. 760 — Cavolinia trispinosa (Dall). 1, gill, 

 Fig. 761 — >Creseis conica (Dall). 



Limacina Cuvier. Shell transparent, with a low spiral and a wide 

 umbilicus : 'several species in the Arctic and Antarctic seas, which form 

 an important food of whales. 



L. arctica (Fabricius) (Fig. 759). Whorls of shell 6; spire low; 

 umbilicus wide; width 4 mm.: Arctic seas, south to New Jersey. 



Family 7. CAVOLINIIDAE. (Pteropoda Thecosomata.) 



Shell and mantle present; shell not spiral, but symmetrical, straight 

 or curved, without operculum; ctenidium and eyes absent; 1 pair of ten- 

 tacles ; mantle cavity ventral ; 2 large fins present as in previous family : 

 about 50 species, all of which are pelagic. 



1. Cavolinia Abildgaard {Hyalea Lamarck). Shell globular, with 

 3 long sharp spines posteriorly; aperture contracted with a slit on each 

 side, through which long appendages of the mantle pass : 10 species. 



C. trispinosa (Lesueur) (Fig. 760). Length 10 mm.; median spine 

 as long as the body; lateral spines only a third as long: Atlantic coast. 



