FOSSIL CIRRIPEDES. 537 



Upper latns. Length 6"8 mm. ; breadth circa 7'5 mm. 

 Rostral latns. Length 6'3 mm. ; breadth 2'6 mm, 

 Rostrum, Length 3'4 mm, ; breadth 2-2 mm. 



Specimen I. 13580. 



Cai'ina. Length circa 20 mm, 



Tergum. Length circa 17 mm. ; breadth 7"5 mm. 



Upper latus. Length 5-9 mm, ; breadth circa 4'2 mm. 



Scales of peduncle. Length from 0-5 mm, to 1*2 mm. ; breadth 

 1'3 mm, to 2 mm. 



Remarhs^ and comparison loith other Species. — The restoration 

 of S. arcuatum (text-fig, 65, 7) is based on the nearly complete 

 capitulum figured on the same page, and, to complete the capitu- 

 lum, a carinal latus and an inframedian latus have been added. 

 The carinal latus figured in the restoration was found amongst a 

 nnmber of detached plates of S. arcuatum from the Cambridge 

 Greensand, and is longitudinally ridged as in the valves of 

 >S'. arcuatum. It possibly belongs to the same species. In any 

 ease the only carinal latera known to the writer from the Lower 

 Cretaceous rocks are of the type figured, although they evidently 

 belong to several diflTerent species. Judging from the hiatus 

 between the carinal latus and rostral latus, an inframedian 

 latus was undoubtedly present, and was probably very like the 

 homologous valve in S.fossula from the Upper Senonian, 



The specimen of *S'. arcuatum here figured (text-fig, 65, G') is, 

 up to the present, the oldest fossil Scalpelhbm from Avhich one 

 can gain any idea of the appearance of the complete capitulum. 

 It comes from the Albian (Gault) of Folkestone, Kent, and the 

 only undoubted valves of Scalpellum older than this occur in the 

 Aptian (Lower Greensand) *", These Lower Greensand forms 

 comprise only three species, two of which — S. simplex Darwin 

 and S, accumiolatum Withers — are respectively i-epresented by 

 a single carina ; the third, ^S. comptmn Withers, is represented 

 by two detached terga. 



Our knowledge of these early forms of Scalpellum is therefore 

 not very extensive, and the fact that they are represented by 

 such a small number of valves, and those only of carinfe and 

 terga, serves to emphasize the importance of this fine example of 

 *S'. arcuatum (text-fig. 65, G). 



A comparison of the carina and tergum of ;S', arcitatum with the 

 corresponding valves of S. SGliduhim Steenstrup, as figured by 

 Darwin (1851, p, 42, pi. i. fig, 8), shows how closely these two 

 species resemble each other. They are evidently related. The 



* This statement is made with full knowledge that certain valves from the 

 Palaeozoic and Jurassic rocks have been referred bj' various authors to the o-enns 

 Scalpellum. There is, however, not sufficient evidence to justify the reference of 

 these valves to the genus Scalpellum. Notwithstanding this, it is possible that 

 some of the Mesozoic Cirripedes referred to Pollicipes may eventually be shown 

 to be ancestral forms of Scalpellum, but this cannot be done until moi'e is known of 

 the various valves comprising the capitulum. 



Proc, Zool, Soc— 1912, No. XXX YI. 36 



