588 MOLLUSCA 



Key to the genera of Tellinidae here described: 



©1 Shell over 12 mm. long. 



6i Shell elliptical ; lateral tooth present 1. Tellina 



62 Shell round or ovate ; no laterals 2. Macoma 



O3 Shell under G mm. in length 3. Gastbanella 



1. Tellina L. Shell slightly inequivalve, oval, rounded in front, 

 with an oblique ridge behind; umbo nearly central; 2 cardinals and usu- 

 ally posterior and anterior lateral in each valve: 300 species, chiefly in 

 the tropics, where the shells are often highly colored. 



T. tenera Say (Fig. 925). Shell 14 mm. long, 9 mm. high, and 3 mm. 

 wide, thin, delicate, white or pinkish in color, polished, sometimes con- 

 centrically banded ; umbo a little back of the middle ; 1 of 

 the cardinals rudimentary in each valve: Gulf of St. 

 Lawrence to west coast of Florida, on sandy beaches; 

 Fig 92^ often common; West Indies. 



Tellina tenera T. tenella Yerrill. Shell same in size and color as 



(Ball). 



above; anterior dorsal margin straight or concave; pos- 

 terior end short and rounded ; umbo at the posterior third : Long Island 

 and Vineyard Sounds in 4 to 10 fathoms. 



2. Macoma Leach. Shell oval, round or triangular, equivalve, 

 swollen, gaping at the ends; 2 weak cardinals; no laterals; anal siphon 

 long; branchial short: 100 species, in all seas. 



M. tenta Say. Shell oval, very convex, thin, white, with pointed 

 umbo; posterior part narrowed; length 15 mm.; height 10 mm.; width 5 

 mm. ; 2 cardinals in the right and 1 in the left valve : Cape Cod to 

 Florida; common in muddy bays; West Indies. 



M. baltica (L.) (Fig. 926). Shell nearly round, thin, slightly nar- 

 rowed behind, 23 mm. long, 18 mm. high, and 9 mm. wide ; 2 cardinals in 



Fig: 926 Fig. 927 Fig. 928 



Fig. 926 — Macoma baltica (Gould). Fig. 927 — Gastranella tumida (Verrill). 

 Fig. 928 — Cumingia tellinoides (Gould). 



each valve: Arctic Ocean to Georgia, very common in shallow water; in 

 muddy bays the shell is thick, of bluish or rusty color, and covered with 

 a dark periostracum, in sandy localities pure white or pinkish or yellow- 

 ish and thin; Pacific coast; Europe. 



3. Gastranella Verrill. Shell minute, elongate, more or less irreg- 

 ular; 2 cardinals in each valve; no distinct laterals; siphons long and 

 separate: 1 species. 



