POLLICIPES. G7 



of the valve ; internally (^), the lines of growth round the upper margins show that the two 

 upper sides and the apex overlapped freely the valves on each side of them. This valve, 

 as stated in the preliminary remarks, has naturally been always mistaken for a scutum ; 

 but the manner in which it has overlapped other valves (as shown by the internal view), on 

 both its upper margins, and the entire absence of all hollow for the adductor muscle prove 

 that this view is quite erroneous. 



The two rostral or anterior small latera resemble each other (the anterior one being a 

 little the smallest), and likewise the largest carinal latera just described ; the external 

 ridge, however, here runs to a much more nearly central point of the basal margin ; and 

 the shorter and more pointed portion of the basal margin is just perceptibly hollowed out. 

 The more pointed end is directed towards the carina. In the first latus this end abuts 

 against (no doubt thus producing) the external ridge on the second latus, which it overlaps. 

 Internally, under the apex, there is a central crest (/), exactly as in the latera of the lower 

 whorl in large specimens of the recent P. mitella, caused likewise by the overlapping of the 

 valves : in the above -described large carinal latera, however, this internal crest is absent, 

 showing that the arrangement of these latter valves differed from that of the two anterior 

 ones. 



With respect to the number of valves in the whole capitulum, it is almost useless to 

 speculate : we have two scuta, two terga, two upper latera, two rostra, and we may, per- 

 haps, infer two carinse, making ten valves, we know of three pair of lower latera, making 

 sixteen valves : I believe there must have existed some other latera, but probably only 

 a few more ; for these valves, especially the carinal pair, are much larger, in proportion to 

 the scuta and terga, than in any recent Pollicipes. Probably the lower latera, together with 

 the sub-rostrum, and perhaps a sub-carina, formed only a single lower whorl. 



Size : in the individual here described, the carina and terga, were equal in length to 

 each other, and "65 of an inch long. In Mr. Bowerbank's collection there is a lower latus 

 of nearly double the size of the same valve in this individual, which shows that this species 

 attains large dimensions. 



Afmities. As before remarked, this species is very closely related to the cretaceous 

 P. glaber, of which it is evidently the representative in the Gault ; the chief difference 

 consisting in the more elongated form and greater size of the upper latera, which, in 

 P. unguis, exceed half the length of the tergum, whereas in P. glaber they are only one 

 third of its length. The carina, in the present species, has its basal margin, perhaps, less 

 pointed, and has a narrow linear channel along its edges ; but I am not at all sure that this 

 latter character does not vary. Lastly, the anterior lower latera in P. unguis are thinner, 

 and rather more convex, with the basal margin more arched and protuberant, with the 

 external oblique ridge very much more central. 



Considering the characters of both species taken together, namely, the two ridges pro- 

 ceeding from the umbo of the scuta to the baso-lateral angle and basal margin, — the 

 triangular shape of the upper latera, — the considerable size of the rostrum, and the ridges 



