48 FOSSIL CIRRIPEDIA. 



the tergo-lateral margin more or less protuberant, but not divided by an angle into two 

 distinct margins. 



f Scuta smooth, or marked only with fine lines of growth. 



A. Scuta without any ridge proceeding from the apex to a nearly middle point of tiie 

 basal margin. 



B. Scuta with a ridge, sometimes faint, proceeding from the apex to a nearly middle 

 point of the basal margin. 



tf . Scuta either longitudinally or transversely (that is in the direction of the lines of 

 growth) ridged. 



As with Scalpellum, the first of the above two paragraphs contains the true generic 

 description, as applicable to recent and fossil species ; the second paragraph has been drawn 

 up as an aid in classifying separated valves. This, the most ancient genus of the Lepadidae, 

 seems also to be the stem of the genealogical tree ; for PoUicipes leads, with hardly a 

 break, by some of its species into Scalpellum villosum j and Scalpellum leads by Oxynaspis 

 into Lepas and the allied genera -. FolUcipes mitella, moreover, is nearer allied to the 

 Sessile Cirripedes than is any other Pedunculated cirripede, except, perhaps, Lithotrya, which 

 is also closely connected with PoUicipes. The six recent species of PoUicipes might be 

 divided into three sub-genera : one containing the P. mitella ; a second, P. cornucopia, 

 elegans wApolymerus; and the third, P. spinosus and serta {nov. spec.) Of the fossil species 

 some, as P. carinatus, dorsatus, validus, &c., are related to the first section ; others, as 

 P. rejlexus and concinnm, to the second section ; and lastly, others, as P.glaher and unguis, 

 perhaps form a distinct section, though more related to P. mitella than to other recent 

 species. As, however, most species are known by only a few of their valves, it is scarcely 

 possible to speak with certainty regarding their finer affinities. 



Descriptio}i .- as in the case of Scalpellum, the following remarks are confined to the fossil 

 species of the genus. In all full-grown recent species the number of valves in the capitulum is 

 very large : this seems to have been the case with the Oolitic P. concinnus, and probably with 

 most other species, but whether with all may be doubted ; from the size of the carinal 

 latera of the lower whorl in P. unguis, I suspect that the total number of its valves cannot 

 have been great. The valves are either smooth or plainly marked by the lines of growth, 

 or they rarely have longitudinal ridges, or transverse ridges corresponding to each 

 periodical zone of growth : no recent PoUicipes has a surface of this latter kind. The 

 valves in PoUicipes are often strong and massive, with their apices projecting freely from 

 the capitulum. 



Scuta generally three- sided, but sometimes, from either the baso-lateral or rostral 

 angles being truncated, there is an additional lower side. The tergo-lateral margin is 

 either straiglit or generally more or less convex, but it is never (as far as I know) divided 

 into two distinct margins, as is always the case with Scalpellum owing to the abrupt 

 ending of the upturned lines of growth. The basal margin is either straight or formed 



