262 Mr. T. H. Withers on 
the Tithonian species Brachylepas (?) fimbriatus and B. (?) 
tithonicus. I have already shown * (1914) that the genus 
Scillelepas existed in the Upper tee (Upper Senonian 
and Danian), and it was then pointed out that, although there 
was no definite evidence, certain of the detached valves 
described as Pollicipes from the Jurassic rocks have much 
resemblance to the valves of Scrllelepas. 
In Polhicipes, Archeolepas, Pycnolepas, and Setllelepas all 
the valves have a downward growth, so that, in the absence 
of definite 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 
only criteria we have in placing S. gaveyt?. 
Undoubted species of Archwolepas lave the carina much 
reduced in size as compared with the remaining capitular 
valves; it is somewhat triangular in shape and slightly 
expanded at the basal angles. Neither the carina nor the 
terga in S, gavey? are at all like the valves in Archeolepas, 
and the presence of a subcarina, which is absent in that 
genus, renders it unlikely that it is a species of Archeolepas. 
There is a superficial similarity in the structure of the 
carina, principally in the prominent transverse growth-ridges, 
with that of Pycnolepas, but the rounded basal margin shows 
it to be of a different type of valve. ‘The tergum and scutum 
are altogether different in structure, thus preventing the 
species being referred with any confidence to the genus 
Pyenclepas. 
S. gaveyi might be referred to Pollicipes, for the carina 
appears to be of much the same shape as the recent species : 
but the absence of definite evidence as to the number of 
valves in S. gaveyi, the fact that the tergum differs markedly, 
and that the impression of the scutum shows that the valve 
was of the same type as in P. oolitieus, makes one hesitate to 
refer the species to Pollic/pes, more especially so since it 
would seem that hardly any of the Jurassic or even Cretaceous 
species can be confidently referred to Pollicipes. 
Now the terga of S. gavey2 are particularly elongate, as are - 
also those of the genus Scillelepas. While there is nothing 
in favour of the reference to Scil/elepas in the character of 
the carina, there is nothing opposed to it; but the most con- 
vincing of the valves is the scutum, of which, unfortunately, 
we have only the impression. This, however, shows it to be 
a valve resembling the scutum of P. coliticus and P. quen- 
stedti, and particularly like the scutum in both the recent and 
fossil species of the genus Scillelepas. 
If the shape and structure of these detached valves be 
* Withers, T. H., 1914, op. cit. p. 192, 
