342 GENUS — LITHOTRYA. 



cup resembles, in essential structure, the valves of the 

 capitulum ; the chief difference being that in the former 

 there is a larger proportion of animal matter or mem- 

 branous lavers. 



After the dissolution of the cups, in L. dorsalis and L. 

 H/wdiojMS, I most distinctly traced the two cement-ducts ; 

 they included the usual darker chord of cellular matter ; 

 they were of rather small diameter, namely, ^oth of an 

 inch. The two (in L. dorsalis) ran in a very irregular 

 course, not parallel to each other, making the most abrupt 

 bends. They passed through the membranous layers, (as 

 seen after dissolution,) and running for short spaces pa- 

 rallel to the component laminae, were attached to them. 

 In their irregular course, these cement-ducts resemble 

 those of Pollicipes mitella, but I could not perceive that 

 any cement had been poured out at the abrupt bends. 

 In one specimen of a basal cup, which I was enabled 

 to examine whilst still attached to the rock, I found 

 under the very centre, (and of course outside the yellow 

 membrane,) a very small area of dark brown cement of 

 the usual appearance. In several specimens of full-sized 

 cups, I was not able to perceive any cement on the external 

 surfaces of the upper and later-formed layers ; hence I 

 believe that the cup is cemented to the bottom of the hole 

 only during the early stages of its formation ; and this, 

 considering its protected situation, would no doubt be 

 sufficient to affix the animal. This probably accounts for 

 the small size of the cement-ducts, and for the facility with 

 which, as it appears, the cups can be removed in an un- 

 broken condition from the rock. In the case, however, 

 of the small, flat, calcareous discs, which are formed whilst 

 the animal is burrowing into the rock, these are attached 

 firmly to the sides of the holes, in the usual manner, by 

 cement. In this cirripede it would be useless to look for 

 the prehensile antennse of the larva under the cup, for the 

 animal, during the formation of the successive discs, must 

 have travelled some distance from the spot on which the 

 larva first attached itself. 



