EAST COAST MARINE SHELLS 



143 



but the more usefiil fins largely replace It. 

 These fins are placed near the mouth and 

 neck. 



When the shell Is present it is 

 usually glassy, often translucent, with 

 dorsal and ventral plate united. Old, worn, 

 or dead specimens often appear opaque. 



The sexes are united, each individ- 

 ual possessing male and female organs which 

 are located on the right side of the neck. 



These mollusks show no affinity 

 with the bivalves. There are certain char- 

 acters which suggest the Cephalopoda but 

 the Pteropoda are unique and deserve com- 

 plete isolation in a separate order. They 

 are possibly closest to the Gastropoda. 



Family Limaclnidae 



Shell minute, spiral, sometimes 

 operculate. The true fry are left-handed 

 and on this account may easily be separated 

 from Atlanta, Carinaria, and other Gastro- 

 pods. 



GENUS LIMACINA Cuvler 1817 



Shell umbillcated, umbilicus mar- 

 ginal; no operculum. 



LIMACINA TROCHIFORMIS Soul. The smallest 

 of the American Pteropods. Diameter 1 mm. 

 N. 42° to S. S8° 



LIMACINA BULIMOIDES Orbigny. Another very 

 small form. Length 2 mm. 

 N. 35° to S. 48° 



LIMACINA HELICINA Phipps. The illustration 

 is of the radula enlarged. 



PI. 68, Fig. 14 



Arctic Seas to Gulf of Maine 



Family Cavoliniidae 



GENUS CAVOLINA Gioeni 1785, Hyalaea 

 Lamarck 1801 



CAVOLINA TRISPINOSA Le Sueur. Shell com- 

 pressed; three straight spines, one longer 

 behind; longitudinally ribbed on ventral 

 face; color whitish, almost transparent, 

 smoky tinted. Length 10 mm. 



PI. 59, Fig. 12 (Shell) 



PI. 74, Fig. 115 



N. 60° to S. 40° 



CAVOLINA LONGIROSTRIS Le Sueur. Shell 

 marked with five concentric ridges, upper 

 face almost hemispherical, dorsal face 

 ribbed, forming in front a long, folded, 

 depressed beak; lateral spines compressed, 

 middle spine truncated and short. Length 

 4 mm. 



PI. 49, Fig. 12 



N. 47° to S. 40° 



CAVOLINA GIBBOSA Rang. Shell somewhat in- 

 flated, ventral face with high sharp ridge, 

 this portion striated, the rest finely 

 reticulated; dorsal face convex, almost 

 smooth or with seven faint ridges; upper 

 lip turned sharply downward; lateral spines 

 short, close together, middle spine stout, 

 short and a little curved upward. Length 

 9 mm. 



PI. 59, Fig. 8 



N. 43° to S. 41° 



CAVOLINA TELEMUS Linne (C. trldentata) . One 

 of the largest forms in this group and 

 often represented in collections. Length 

 18 mm. 



PI. 74, Fig. 113 



PI. 59, Fig. 9 



N. 40° to S. 40° 



CAVOLINA UNCINATA Rang. Much swollen ven- 

 trally, surface finely and evenly reticu- 

 lated, fine ridges in front; dorsal surface 

 with three low radiating ribs, evenly round- 

 ed at aperture, turned downward; lateral 

 spines compressed and curved a little back- 

 ward; middle spine short, stout and turned 

 upward. Color pale amber. Length 9 mm. 



PI, 74, Fig. 116 



N. 40° to S. 40° 



CAVOLINA INFLEXA Le Sueur. Shell long, com- 

 pressed, ventral face a little inflated; 

 dorsal face indistinctly three ribbed; lat- 

 eral spines small, turned backward slightly; 

 central spine long, stout and curved upward. 

 Length 5 mm. 



N. 40° to S. 42° 



GENUS CRESEIS Rang 1828 



CRESEIS ACICULA Rang (S. recta of authors). 

 Pelagic. 



PI. 74, Fig. 118 



N. 48° to S. 40°; Gulf of Mexico 



