204 THE SEA SHORE 



come in its way into a flask-shaped cell. The opening of the 

 burrow is shaped like an hour-glass, the two expansions serving 

 for the protrusion of the siphonal tubes, and the neck of the flask- 

 shaped abode is usually lined with a calcareous layer that pro- 

 jects slightly to afford further protection to the extended siphons. 

 Although this species is very common on some parts of our coast, it 

 is seldom obtained without the aid of a dredge, for it usually lives 

 at a depth of from five to ten fathoms; and when found it is 

 generally no easy matter to extricate them from their holes, to the 

 sides of which they often cement their shells. 



The genus Saxicava contains a few species that drill holes, 

 often several inches deep, in shells and stone, and frequently do 

 great damage to breakwaters and other artificial structures. The 

 foot is usually provided with a byssus by which the animal fixes 

 itself to a little projection on the side of its barrow. The species 



FIG. 137. 1. Thracia phascolina. 2. Thracia pubescens, SHOWING 

 PALLIAL LINE 



are to be found from low -water mark to a depth of one hundred 

 fathoms or more. 



The next family, named Anatinidce, contains a number of 

 molluscs that burrow in mud or sand or live in seclusion in the 

 crevices of rocks. Their shells are thin, with a granulated outer 

 surface, and the valves are united by a thin external ligament. The 

 inner surface is pearly, the pallial line usually sinuated, and both 

 valves are pitted for the reception of the somewhat stout internal 

 cartilage. The mantle lobes are united, as are also the siphons to 

 a greater or lesser extent ; and there is only one gill on each side. 



Some of the common species of this family are popularly known 

 as Lantern shells, and perhaps the most familiar of these is 

 Thracia phaseolina, the specific name of which is given on 

 account of a fancied resemblance of the shell to a bean. The shell 

 is very fragile, and although large numbers may often be seen 

 stranded on sandy beaches, but few of them are perfect specimens. 



