154 T. H. Withers—New Chalk Cirripedes. 
Holotype.—Left tergum (B.M., I. 13,403), Caleb Evans Collection. 
Length of valve about 8mm., breadth 4mm., length of occludent 
margin about 5 mm., length of scutal margin 4mm. 
Horizon and Locality.—Aptian, Lower Greensand: Sevenoaks, Kent. 
Another specimen, a right tergum (B.M., 13,404) from the same 
collection, locality, and horizon, undoubtedly belongs to this species. 
Both terga have their basal angles broken, but judging from the 
adjoining outline of the margins there is little doubt that they were 
rounded. The left tergum is taken as the holotype, as it is the most 
perfect. 
Comparison with other Species.—Under the name Pollicipes radiatus, 
J. de C. Sowerby (1836),1 figured two valves of a Cirripede, which 
appear to be of different species. The only description given is: 
‘‘ Valves wedge-shaped, flat, marked with sharp, elevated rays, 
diverging from their apices.” Darwin in his monograph (1851, p. 40) 
says of Scalpellum arcuatum: ‘‘This species appears to come nearest 
to Pollicipes radiatus of J. de C. Sowerby . . . but besides that that 
species comes from the Lower Greensand, the lower angle is much 
more pointed; the upper figure of the two appears to be something 
wholly different.” Further, Darwin (1851, p. 80) says: ‘‘The 
P. radiatus of the same author (J. de C. Sowerby) of the Lower 
Greensand (pl. xi, fig. 6) is unknown to me; the tergum figured is 
like that of S. arcuatum; the upper figure, if a scutum, is very 
remarkable.’’ As these two valves figured by J. de C. Sowerby 
apparently belong to different species, it seems advisable to fix the 
holotype, and I therefore select the upper figure as the type of 
Pollicipes radiatus. It may be that Sowerby’s lower figure repre- 
sents a valve of S. comptum, but since the specimen cannot now be 
traced, and the figure and description are quite insufficient for exact 
determination, it is advisable to establish a new species for the 
specimens mentioned above, and to place in it provisionally the 
original of Sowerby’s lower figure. 
S. comptum may be compared with the Albian S. arcuatum, Darwin 
(1851, p. 40, pl. i, fig. 7), from the Gault, and S. fossula, Darwin 
(1851, p. 24, pl. i, fig. 4), from the Senonian (Bel. mueronata-zone) 
of Norwich. Both agree with it in having a delicate furrow 
extending from the apex to the basal angle; S. fossula further agrees 
in having a slight longitudinal ridge dividing the occludent portion 
into two parts. This ridge, however, is not raised as in S. comptum. 
In S. fossula the surface is not ornamented with raised longitudinal 
ridges, but is almost smooth; the carinal portion of the valve is 
proportionately much narrower, the apex and the basal angle are 
much more pointed, and the scutal margin is not sinuous. S. arcuatum 
differs by the absence of the raised longitudinal ridge extending from 
the apex to the scutal margin, and by the lines of erowth being much 
more sinuous on the occludent portion. The general outline is more 
1 Descriptive notes respecting the shells figured in pls. xi to xxiii, Appendix A, 
to W. H. Fitton, ‘‘ Observations on some of the Strata between the Chalk and the 
Oxford Oolite in the South-East of England’: Trans, Geol. Soc., ser. 1, vol. iv, 
pl. xi, fig. 6. 
