PHOLADIDiE. 125 



pick, are employed in collecting them, either to sell in the mar- 

 ket, or for fishermen's bait. They are almost entirely littoral, 



"Entomb'd upon the very hem o' the sea." 



The property which they possess of shining in the dark is very 

 remarkable. 



CYRTOPLEURA, Tr3^on, 1862. Margins of the valves emarginate 

 anteriorly, forming a short, wide hiatus. 3 sp. U. S., Panama, 

 Philippines. 



Dactylina, Gray, ISiT. 



Distr. — 3 sp. D. dactylus, L. (civ, 58, 59). Europe. 



Shell oblong-oval, anteriorly emarginate ; cardinal margin 

 reflected over the back of the shell, from which it is separated 

 by numerous horizontal plates, covered by two dorsal accessory 

 valves, arranged side by side, their nuclei at their outer margins, 

 posterior to the centre. 



Siphons naked to the base ; orifice of the branchial siphon 

 cirrated, that of the anal siphon simple or crenulated. 



The common piddock is used for bait on the Devon coast 

 (England) ; its foot is white and translucent when fresh, like a 

 piece of ice ; the hyaline stylet lodged in it is large and curious'. 



GITOCENTRUM, Tryou, 1862. Valves not emarginate anteriorly, 

 but regularly rounded, forming a long, narrow hiatus ; nuclei of 

 the dorsal valves anterior, situated nearer the inner margin. 

 2 sp. Southern U. S., W. Indies, Chili. D. campechensis^ Gmel. 



Barnea (Leach), Risso, 1826. 



Distr. — 9 sp. Australia, Burmah, Red Sea, Europe, Patago- 

 nia, Philippines. B. Candida, Linn. Europe. 



Shell oval-oblong ; anteriorly gaping ; a single lanceolate dorsal 

 accessory valve ; umbonal process reflexed, closely applied. 



barnea (typical). Anterior margins regularly rounded, form- 

 ing a long, narrow hiatus. 



anchomasa. Leach. Yentral anterior margin of the valves 

 emarginate, the hiatus short and wide. B. parva, Pennant: 

 Europe. 



MoNOTHYRA, Tryou, 1862. 



Distr. — M. orientalis, Gmel. (civ, 60). India. 



Dorsal valve ovate-cuneiform ; reflexed umbonal processes cel- 

 lular beneath. 



Xylophaga, Turton, 1822. 



Etym. — Xulon, wood, phago, to eat. 



Distr. — 3 sp. Norway, Britain, Western South America, 

 Mergive Is. Bores an inch deep, and across the grain, in float- 

 ing wood, and timbers which are alwa3^s covered by the sea. A 

 few tertiary species, X. dorsa'Js, Turton (cv, 7t-Y9). England. 



Shell globular, with a transverse furrow ; gaping in front, 



