left valve, broadly compressed, rather rounded, and pro- 

 jecting almost vertically ; a cardinal pit in the other valve. 

 Ligament internal, inserted in the prominent tooth and 

 the corresponding pit. 



M. TRUNCATA. ^Turt. Lin. Pen. Brit. Zo., vol. 4, pi. 41, 

 fig. 14. Stew. Elem., vol. 2. p. 336. Mont. Test. Brit., 

 vol. 1, p. 32, Fleio. Brit. An. p. 162. Rare. 

 ANATINA. 



GENERIC CHARACTER : Shell transverse, with nearly 

 equal valves, gaping at one or both sides; one naked, 

 broad, spoonshaped, cardinal tooth, projecting internally, 

 in each valve, and receiving the ligament. In many species 

 a lamina or falcated rib runs obliquely below the cardinal 

 teeth. 



A. MYALIS. Mya Pubescens. Mont. Test. Brit., vol. 1, 

 p. 40. Amphisdesma P. Flem. Brit. An., p. 431. 

 Anatina M. Crouch's Introd., pi. 4, fig. 1. 

 Montagu says, "this species is not uncommon, of small 



size, taken up with sand from Falmouth harbour — one we 



received from Plymouth, taken by dredging, was 2 inches 



broad, and 1| long." It is otherwise rare; but I obtained 



it at Falmouth, above 2^ inches broad. 



A. DECLIVIS. Marked for me at the British Museum, 

 but which I am not able with confidence to refer to any of 

 the usually received synonyms of this shell: considered, as 

 it usually is, as the young state of the last species. Pennant, 

 Montagu and Fleming, are entirely at variance on this 

 subject; and until more information is obtained, it is best 

 to report it simply, as not of common occurrence within 

 the sphere of my observation. 



SECTION II. 



The foot small, compressed ; Lobes of the mantle scarcely 

 or not at all united in front. Lateral gaping of the shell 

 generally inconsiderable. m 



M ACT RACE A. 



The shell with equal valves, generally gaping at the lateral 

 extremities. Ligament internal, with or without an external 

 ligament. 



LUTRARIA. 



GENERIC CHARACTER: The shell with unequal sides, 

 transversely oblong or rounded, lateral extremities gaping; 

 hinge with one tooth folded in two ; or two teeth, one of 

 which is simple, with an adjoining, deltoid, oblique pit, 

 projecting inwards; no lateral teeth. Ligament internal, 

 affixed in the pits. 



* L. VULGARIS. Mactra Lutraria. Turt. Lin. Pen. 

 Brit. Zo., vol. 4, pi. 52, fig. 44. Stew. Elem., vol. 2, 



