.532 



MR. T. H. WITHERS ON 



This species was founded on a carina and tei-gvim from the 

 Cenomanian (Grey Chalk) of Dover. The tergum cannot now be 

 found, but the carina, which Darwin considered to be the typical 

 valve of the genus and can therefore be regarded as the holotype, 

 is in the British Museum (Natural History) registered 38461. 



Diagnosis. — Carina with three prominent, rounded, longi- 

 tudinal ridges on its tectum — one central, and one on each side 

 separating the tectum from the parietes; intraparietes bent 

 inwards almost at right angles, the inner margins meeting a 

 short distance below the apex, upper part of valve solid and 

 projecting freely. 



Description of Carina. — Carina narrow, widening very gradu- 

 ally from the apex, considerably bowed inwards, basal mai'gin 

 obtusely angular. Tectum flatly-arched transversely, with a 

 central, prominent, rounded ridge extending from the apex to 

 the basal margin, and bounded on each side by a slightly coarser 

 but flatter ridge on the angle separating the tectum from the 

 parietes. Parietes narrow, less than half the width of the tectum, 

 bent almost at right angles to the tectum, slightly concave. 

 Intraparietes very narrow, bent inwards almost at right angles, 

 the inner margins meeting about one-sixth the length of the 

 valve from the apex ; the upper part of the valve is solid, niid 

 must have projected freely to the extent indicated by the meeting 

 of the intraparietes. Lines of growth plainly marked. 



ScALPELLUM ARCUATUM Darwin. (Text-fig. 65.) 



1851. Scalpellum arcuatum C. R. Darwin, Pal. Soc. Monogr. 



Foss. Lepadidag, p. 40, pi. i. fig. 7. 

 1854. Scalpellum arcuatum C. R. Darwin, Ray Soc. Monogr. 



Sub-class Cirripedia, Balanidae, Synopsis et Index 



Systematicus, p. 633. 

 1854. Scalpellum arcuatum J. Morris, Cat. British Fossils, 2nd ed. 



p. 96. 

 1865. Scalpellum arcuaturti J. W. Salter & H. "Woodward 



Cat. & Chart Foss. Crustacea, p. 27, pi. i. fig. 14. 

 1877. Scalpellum arcuatum H. Woodward, Biit. Mus. Cat. Brit. 



Foss. Crustacea, p. 142. 

 The species S. arcuatum was founded on three detached valves, 

 namely, ca,rina, scutum, and tergum, from the Gault of Folke- 

 stone, Kent, These valves were considered by Darwin to belong 

 to the same species, and the material now to be described pi'oves 

 such to be the case. Darwin further stated that these valves 

 were in the Bowerbank Collection. This collection was acquired 

 in 1865 by the British Museum (Natural History), and among 

 the specimens are three valves, a carina (I. 13796), a scutum 

 (I. 13797), and tergum (I. 13798), mounted together on Bower- 

 bank's original tablet, and labelled in Darwin's handwriting 

 " S. arcuatum.''^ The carina has been much broken, presumably 

 since Darwin described it, but the scutum and tergum are in good 



