the, Cirri/tede G^nuft Sfrnmoiitum. 73 



Description of Shell. 



Capitulum. — This is small when compared with the size 

 aud breadth of the peduucle, its length lieing about onc- 

 fonrth that of tiio shell ; evidently the pircater part of the 

 animal's body was lodged in the peduncle as in Lithotrija 

 and Iblii. 



Scutum subtriangular in outline, with the tergo-lateral 

 and basal margins nearly straight and almost at right angles 

 to each other ; the growth-lines in the lower part of the 

 valve follow the outline of the tergo-lateral and basal 

 margins. The umbo is situated at a variable distance from 

 the apex, and in the more advanced of the Turonian forms 

 is about one-third the distance from the apex ; in the Seno- 

 nian species, S. haworthi, the umbo is situated at least one- 

 half the distance from the apex even in quite young valves, 

 and the more advanced forms have the upper half of the 

 valve more developed. From the umbo to the apex runs a 

 depression from which the upper part of the occludeut margin 

 rises up. In the figured .specimen of S. haworthi and 

 in others on the two slabs there is^ on the inner surface, a 

 deep pit for the adductor muscle. 



Upper lahis almost flat, having the outline of an isosceles 

 triangle, with the scutal margin, which abuts against the 

 tergo-lateral margin of the scutum for its whole length, 

 rather more obliquely inclined and slightly longer than the 

 tergal margin. The valve evidently overlapped the tergum 

 and scutum very slightly by its edges, and the growth-lines 

 are straight and parallel. Darwin said of this valve "The 

 first latus now answers to the upper latus in Sculpellum, 

 but it is interposed to quite an unprecedented extent between 

 the scutum and tergum.^' It is, however, not more so than 

 in the recent Pollicipes mitella, or in the l.iter-discovered 

 Cretaceous cinipede Zeurpnatolepas mockleri, which perhaps 

 is more comparable, since the upper part of the upper latus 

 in P. mitella really overlaps the scutum and tergum for the 

 greater part of its extent. 



Teryuiii subtriangular, somewhat convex, with the carino- 

 lateral and the upj)er occludent margins slightly rouiuled, 

 and the basal margin rather more so. The growth-lines are 

 convex, and on the upper occludent margin curve sharply 

 upwards towards the apex. 



Cariual latus ohliqucly triangular, rather like the upper 

 latus, except that the tergal margin is more obliquely inclined 

 and the basal margin more rounded, the valve being slightly 

 inclined towards the tergum. 



