600 



MOLLUSCA 



SUBORDER 7. ANATINACEA. 



Shell thin, white and pearly; hinge with or without teeth; ligament 

 external; mantles united, except where the foot protrudes; 2 adductor 

 muscles; pallial line variable; siphons mostly united: 11 families, all 

 marine, including many degenerate forms, which may lack certain organs, 

 as the foot, adductor muscles, labial palps, and gills. 



Key to the families of Anatinacea here described: 



a s No spatulate hinge lamella. 



&! Pallial sinus slight or absent 1. PANDOBIDAE 



fc a Pallial sinus angulated 2. LYONSHDAE 



c a Hinge lamella in each valve 3. ANATLNIDAE 



FAMILY 1. PANDOBIDAE. 



Shell free or fixed, inequivalve, pearly inside, semi-lunar or trian- 

 gular in shape ; ligament often with a calcareous ossicle ; pallial line with 

 or without a small sinus ; siphons short, united except at the end ; mantle 

 margins united : about 5 species on the Atlantic coast. 



CLIDIOPHORA Carpenter. Shell thin; valves closed, attenuated be- 

 hind; right valve flat, with a diverging ridge; left valve somewhat con- 

 vex, with 2 diverging grooves at the hinge ; a slight pallial sinus : numer- 

 ous species. 

 I 



Fig. 948 



Fig. 949 



Fig. 948 Clidiophora triliniata (Gould). 1, siphons; 2, foot. 

 Fig. 949 Lyonsia hyaUna (Gould). 



0. trilineata (Say) (C. gouldiana Ball) (Fig. 948). Shell rounded 

 in front, hinder end curved upwards, making the dorsal margin straight 

 or concave ; length 32 mm. ; height 17 mm. ; width 5 mm. : Nova Scotia to 

 Texas, in shallow water; common. 



FAMILY 2. LYONSHDAE. 



Shell thin, slightly inequivalve, the left valve being the larger; 

 pallial sinus obscure; hinge teeth absent; hinge with a narrow ledge 

 within each valve, to which adheres an ossicle; siphons very short: 

 several genera. 



LYONSIA Turton. With the characters of the family: 18 species. 



L. hyalina (Conrad) (Fig. 949). Shell ovate, pearly, and transpar- 

 ent; anterior end rounded; posterior end elongated; dorsal line nearly 



