Qapers, Piddocks, and Ship-worms 175 



base of Ccach. The white foot is tongue -shaped, 

 extensible, and grooved for the production of a 

 byssus. It is not a common shell, but it occurs all 

 round our islands on sand between 4 and 86 fathoms. 

 Where these conditions exist it may also be looked 

 for in the stomach of the Red Gurnard. It is about 

 If inch in length. 



The species of Thracia have nearly oval, more 

 symmetrical, and somewhat flattened, thin shells, 

 with a free ossicle as in Lyonsia. The shells gape 

 behind to allow of the continuous extrusion of the 

 long separate siphons. The Thin Lantern - shell 

 {T. prcetemds) has the right valve less flat and a 

 trifle larger than the left, which it 

 slightly overlaps. It is finely 

 marked with lines parallel to the 

 edp-es of the shell, and the hinder 

 slope is also studded with minute 

 tubercles. The shell itself is white, ^^. , , , „ 



Thin Lantern-shell 



but the epidermis is of a creamy (two-thirds nat. size) 

 tint. The dark coloured ligament 

 behind the hinge is so small that it cannot be seen 

 in dried specimens. Attached to the hinge-plate 

 is a spoon-like receptacle for the golden cartilage. 

 The ossicle is sickle-shaped. The animal, includ- 

 ing the tongue-shaped foot, is white. It occurs in 

 sand on many parts of our coast from extreme low 

 water to 60 fathoms. It measures about IJ inch 

 across. The Papery Lantern-shell (T. iDapyracea) is 

 smaller than the last, much thinner, less equivalve, 

 and more convex. Ligament pale and large; carti- 

 lage more brown than golden, its pit or spoon more 

 oblique; the ossicle shaped like half a ring. The 

 12 



