202 Mr. T. H. Withers on 



tlip Tiflioniiin species Brnchylejms (?) fimhr'iotns and B. (?) 

 ti'thnnirufi. I have already shown * (1914) that the genus 

 Scilhrlepas existed in tlie Upper Cretaceous (Upper Senonian 

 aTid Danian), and it was then pointed out tli;it, altliouj^h there 

 w.is no definite evidence, certain of the detached valves 

 described as PoUicipes from the Jurassic rocks have much 

 resenihhince to the valves of Scilhvlepns. 



In J'oJUcipeSj Archwolcpas, Pycnolepas, and SciUcelepaa all 

 the valvos have a downward g'lowth, so that, in the absence 

 of definitf evidence as to their number and disposition, all 

 that one has to go by in referring detached plates to either 

 of those genera is their shape and structure. These are the 

 onlv critciia we have in placing S. gnveyi. 



Undoubted species of Archccokpas have the carina mui-h 

 reduced in size as compared with the remaining capitular 

 valves; it is somewhat triangular in shape and shghtly 

 expanded at the basal angles:. Neitlier the carina nor the 

 torga in S. gaveyi i\re at all like the valves in Archaohpas^ 

 and the presence of a subcarina, which is absent in that 

 g.Mius, renders it uidikely that it is a species of Archceo/e/tas. 



There is a supeificial similarity in the structure of the 

 carina, princi|)ally in the prominent transverse growth-ridges, 

 with that o{ Pycnolepcs^ but the rounded basal n)argin shows 

 it to be of a different typi? of valve. The tergum and scutum 

 are altogether different in structure, thus preventing rlie 

 species l)eing refcned with aiiy coiifilence to the genus 

 Pyni lepas. 



S. gaveyi might be referred to Pollicipes, tor the carina 

 appears to be of much the same shape as the recent spi cies ; 

 but the absence of definite evidence as to the numiier of 

 valves in S. gaveyi, the fact that the tergum differs inarkedl}-, 

 and that the impression of the scutum shows that tlie valve 

 was of the same type as in P. ooUlicus, makes one hesitate to 

 refer the species to Pollicip($, more especially so since it 

 would seem that hardl}- any of the Jurassic or even Cretaceous 

 species can be confidently referred to Pollicipes. 



Now the terga of S. gaveyi are pariii-ularly elongate, as are 

 also those of the f>enus AS(i//a'A^)rt.<f. While there is nothing 

 in Javour ot the reference lo iScilUi'lepas in the cliaracter t)f 

 the carina, there is nothing opposed to it ; but the most con- 

 vijicing of the valves is the scutum, of which, nnfortunalel}', 

 wc have only the impression. Tliis, however, shows it to l)e 

 a valve resembling the scutum of P. oolilicus and P. <juen- 

 uleciii, and particularly like the scutum in both the recent and 

 fossil sj)ecies ol the genus Scillalepas. 



If the shape and structure of these detached valves be 



* Witliers, T. II., 1914, op. cit. p. 192. 



