344 GENUS LITHOTRYA. 



the Cirripecle. Owing to the thinness and fragility of 

 this membrane, the basal attachment of the Cirripede is, 

 no doubt, chiefly effected by the unusually strong lon- 

 gitudinal muscles ; and the necessity of a surface of attach- 

 ment for these muscles, stronger than the external mem- 

 brane of the peduncle, probably is one of the final causes 

 of the basal calcareous disc and cup, and likewise for the 

 unusual manner in which the valves of the capitulum are 

 locked together by folds and small roughened projections. 

 The basal discs and cup, however, apparently serve for 

 several other purposes, namely, for raising the animal a 

 little in its burrow, (which is narrow and pointed at the 

 bottom,) at that period of growth when it has ceased to 

 burrow downwards, but still increases in diameter ; also 

 for carrying the animal, as over a bridge, across any pre- 

 existing cavity in the rock; and lastly, perhaps, for removing 

 lower down, in the intervals of exuviation, the point of 

 attachment for the longitudinal peduncular muscles. 



Position of the animal in the rock, and its power of ex- 

 cavation. — A specimen of rock, two or three inches square, 

 in Mr. Cuming's possession, is full of Lithotryas ; the 

 cavities extend in every possible direction, and several 

 were parallel, but with the animals in reversed positions ; 

 the same thing is apparent in some specimens of Mr. 

 Stutchbury's, and it was evident that the positions 

 occupied by the animals w 7 ere entirely due to chance. 

 In Mr. Cuming's specimen of rock, aconsielerable portion 

 of the external surface is preserved, and here it can be 

 seen that many of the specimens have their capituluins 

 directed from the external surface directly inwards. These 

 individuals, which were of full size, must have preyed on 

 infusoria inhabiting the cavities of the porous, calcareous 

 rock. On the other hand, I have seen some young 

 specimens of L. dorsalis with their valves not at all rubbed, 

 and others of full size with uninjured Balani and corallines 

 on the tips of the valves, and again a specimen of L. trim- 

 cala with minute pale-green seaweed on the summit of 

 the capitulum, — all which appearances induce me to 



