278 GINGLYMACONCHA. AMPHIDESMAD. 
1. AmpPpHIDESMA GOODALLIANA. 
Shells white, pellucid, somewhat prismatic, striolated con- 
centrically, gradually rounded behind. Length three-eighths 
of an inch; height one and a half the eighth of an inch. 
Mya ferruginosa, Mont. Supp. 22; Dill. Dese. Cat. 46; Turt. 
Conch. Dict. 102? 
A. Goodallit is nearly allied to 4. prismatica, from which 
it may at once be distinguished by the gradual rounding of its 
posterior extremity. 
It is by no means uncommon on the southern coast of Devon, 
and is always found in deep water. It has been taken at Bar- 
mouth in Wales by the Provost of Eton. . 
Colour white; its hinder extremity generally more or less 
incrusted with a ferruginous deposit, from which it was impro- 
perly named ferruginosa by Montagu, whose figure has not the 
least affinity with the shell bearmg that name in his collection. 
2, AMPHIDESMA PRISMATICA. 
Shells pellucid, prismatic, concentrically striolated, gradually 
attenuated behind. Length seven-eighths of an inch; height 
nearly half an inch. Colour whitish ; surface very glossy. 
Ligula prismatica, Mont. Test. Brit. Supp. 23. t. xxvi. f. 3 ; 
Flem. Edinb. Encycl. vii. 88. 
Amphidesma prismatica, Lam. Hist. Nat. des Anim. sans Vert. 
v. 492. 
Mya prismatica, Dill. Desc. Cat. 47; Turt. Conch. Dict. 103. 
This beautiful species is by no means uncommon on the 
sandy coasts of the lower parts of the Frith of Forth, especially 
after storms, when they are often thrown on shore in great 
plenty. Montagu found it on the coast of South Devon, where 
it was likewise taken by Mr. Cranch. I found a few dead spe- 
cimens near Clonikelty in Ireland. 
Dr. Goodall has found it several times in the stomach of the 
Common Plaice, Platessa Rondeletii. 
