118 Prof. W. B. Benham — A Giant Fossil Cirripede. 



of Scalpellum or of Follicipes. Of the former, only the rostrum of 

 one fossil species is known, though, as Darwin pointed out, others 

 probably possessed it. Amongst living species some have and 

 others have not a rostrum. In Pollicipes, he says, the rostrum 

 " resembles the carina, but is shorter and proportionately broader." 

 Of the sub-carina we have practically no information. 



The form of the latera is very varied in both genera, but only 

 in a few cases are the lines of growth straight, as in P. glaber 

 (pi. iii, figs. 10/, it), where it is nearly a right-angled triangle. In any 

 case, it seems unlikely that these valves will have a diagnostic value. 

 It occurred to me that some relation in length might exist between 

 carina and scutum, and that a comparison of this relation in 

 Scalpellum on the one hand and Pollicipes on the other might aid 

 me in determining the genus of the fossil. 



But an examination of the material contained in Darwin's 

 monograph of the fossil forms soon showed the unreliability of 

 this method of investigation as applied to them, for it is extremely 

 rare to find a complete capitulum or a set of valves in situ which 

 can be, without any doubt, attributed to an individual. Indeed, only 

 two species of Scalpellum and one of Pollicipes in this condition are 

 recorded by him. 



Further, even in the case of figures of the entire capitulum of 

 living species it is not always possible to measure with absolute 

 accuracy the various valves. Nevertheless, from the figures given 

 below, derived from measurements of Darwin's and Hoek's repre- 

 sentations of the species, a certain proportion — not by any means 

 a constant proportion, however — may be deduced in regard to the 

 relative lengths of carina to scutum. 



It will be seen that in Scalpellum the carina is always longer, 

 usually much longer, than the scutum ; whereas in the case of 

 Pollicipes these two plates are much more nearly, or even actually, 

 of the same size. 



[Length of capitulum, 100.] 

 Scalpellum. Length of carina. Length of scutum. 



■vTilgare 



rostratum 



oruatum 



Peronii 



rutilum 



Stroemii 



Japonicum 



recurvirostris 



Darwinii 



regium ... 



eximiuni 



gigas_ ... 



tritonis 

 Pollici2}es. 



spinosus 



cornucopia 



polymerus 



In attempting to apply this method of comparison to the valves 

 under discussion, we are in this dilemma, that we do not know— in 



