T. H. Withers — The Cirripede Brachylepas cretacea. 357 



surface of the basal ledges. In C. polymerus the outer whorls of 

 valves are quite thin at their base, and there is a definite space 

 bounded by the concave inner margin of each valve, the basis being 

 membranous. Only two other species of Catophragmus besides 

 C. polymerus have yet been discovered, namely, C. imhricatus, Sowerby, 

 and C. Danvini, Pilsbry ; the basis of C. Darwini is unknown, while 

 that of C. imhricatus is calcareous. The basis of B. Naissanti was 

 probably membranous, and in addition the basal ledges of tlie outer 

 whorls of valves together formed, a narrow shelf or platform round the 

 base of the capitulum. This shelf, however, is formed by the ingrowth 

 of the valves and by their interlocking. In the Balanidse proper 

 {Balanus) the calcareous basis is a separate part of the shell, and is 

 added to exteriorly during the growth of the upper compartments. 



Darwin^ lias already observed how nearly related P. mitella is to 

 the sessile Cirripedes, and of Catophragmus ^ he remarked — 



"This genus is very remarkable among sessile Cirripedes, from the eight 

 normal compartments of the shell being surrounded by several whorls of 

 supplemental compartments or scales : these are arranged symmetrically, and 

 decrease in size but increase in number towards the circumference and basal 

 margin. A well-preserved specimen has a very elegant appearance, like certain 

 compound flowers, which when half open are surrounded by imbricated and 

 graduated scales. The Chthamalinse, in the structure of the mouth and cirri, 

 and to a certain extent in that of the shell, fill up the interval between the 

 Balaninse and Lepadidse ; and Catophragmus forms, in a very remarkable manner, 

 the transitional link, for it is impossible not to be struck with the resemblance 

 of its shell with the capitulum of Pollicipes. In Pollicipes, at least in certain 

 species, the scuta and terga are articulated together — the carina, rostrum, and 

 three pairs of latera, making altogether eight inner valves, are considerably 

 larger than those in the outer whorls — the arrangement of the latter, their 

 manner of growth, and union, all are as in Catophragmus. If we in imagination 

 unite some of the characters found in the different species of Pollicipes, and then 

 make the peduncle so short (and it sometimes is very short in P. mitella [see 

 Text-fig. 2]) that the valves of the capitulum should touch the surface of attach- 

 ment, it would be impossible to point out a single external character by which 

 the two genera in these two distinct families could be distinguished : but the 

 more important differences in the arrangement and nature of the muscles, 

 which are attached either to the opercular valves or surround the inside of the 

 peduncle, would yet remain." 



Whilst, as Darwin points out, tlie Chthamalinae ( Catophragmus) link 

 up the Lepadidae with the Balanidae, so the fossil B. Naissanti 

 presents features in common with the Lepadidae as represented by 

 Pollicipes mitella, and the Balanidse as represented by Catophragmus 

 of the sub-family Chthamalinae. The finding of the remaining valves 

 of the capitulum proves that the upper whorl of valves had in 

 B. Naissanti precisely the same structure and arrangement as in the 

 recent P. mitella, and in this respect it is allied to Pollicipes, although 

 the carina and rostrum by their structure and near equality in size 

 suggest that the animal was assuming a more sessile condition of 

 growth. In the presence of several whorls of imbricating plates at 



^ "A Monograph on the Fossil Lepadidae": Paleeontographical Society, 

 1851, p. 48. 



- " A Monogi-aph of the Sub-class Cirripedia, the Balanidse, etc." : Bay 

 Society, 1854, pp. 485-6. 



