CATOPHRAGMUS IMBRICATUS. 491 



no difference from C. polymerus in the shell, excepting that in the 

 small specimen of C. imbricatus, there would appear to exist fewer 

 whorls. The opercular valves are likewise closely similar : in the 

 scuta, however, of the young specimen in the present species, the 

 articular ridge seems to be a little broader, but this is so variable a 

 character that no confidence can be placed in it : these valves, more- 

 over, externally have a broad furrow along the middle, running from 

 the apex to the basal margin, which is not the case with the scutum of 

 C. polymerus ; but then I have often seen, in young specimens of 

 Balanus, a similar furrow, which is quite absent in full-grown speci- 

 mens. When we come to the basis we find a good diagnostic character, 

 for here it is calcareous : it is rather thin, solid, and white ; towards the 

 outside it is pitted with small cavities, corresponding with the small 

 teeth on the basal edges of the compartments. The latter adhere 

 firmly to the basis. The central internal surface is covered by an 

 irregular network of imbedded cement-ducts, some of which bifur- 

 cate. From the description here given, it will be seen that any figure 

 would have been superfluous, the last species having been so well 

 illustrated. 



Mouth. — I can point out no difference, excepting that the palpi are 

 here more oval or less truncated at their ends ; and that the lower 

 corner of the maxillae seems to be more prominent. In the Cirri, the 

 rami of the first and second pairs are nearly equal in length : none of 

 the spines are coarsely pectinated. In the four posterior pairs of cirri, 

 instead of a tuft of small spines on each segment between the pairs 

 of main spines, there are only a few minute intermediate spines : the 

 dorsal tufts are also here smaller, but are, as in the last species, com- 

 posed of short thick, and longer thinner spines. 



Caudal Appendages. — This is the only species of sessile cirripede, 

 with the exception of the two species of Pachylasma, which possesses 

 these organs : they are situated on each side of the anus in the usual 

 position : they are minute, equalling in length only the lower segment 

 of the pedicel of the sixth cirrus : in a specimen in which the rami of 

 the sixth cirrus had eighteen or twenty segments, these appendages 

 consisted of only three tapering segments, supporting a few thick 

 spines. 



Branchice.. — I believe I discovered these, consisting of two minute 

 pouches, placed at the carinal end of the sack : if this observation be 

 correct, this species differs from C. polymerus in the much smaller size 

 of these organs. 



