498 Sie s&s Withers—Pollicipes levis, Sby. 
is the well-marked grooves, of which there are eleven on the portion 
preserved. 
Length 10:5 mm., greatest breadth 3°5 mm. 
Measurements.—As all the valves are slightly broken, it is impossible * 
to give accurate measurements, but those given probably err very 
little. The broken parts are indicated in the figures. 
Comparison with other Species.—The scutum of Pollicipes imbricatus 
agrees with that of P. elongatus, J. Steenstrup (1837), from the Upper 
Chalk (Danian) of Denmark, in its general outline, and in having the 
wide, regularly spaced, well-marked grooves about the same distance 
apart as the growth-lines of P. elongatus. It is distinguished from 
P. elongatus, among other characters, in the occludent portion of 
the valve being twice the width of the tergo-lateral portion. 
In P. elongatus the occludent and the tergo-lateral portions are the 
same width. The tergum of P. imbricatus is altogether different 
from that valve referred to P. elongatus, and therefore need not be 
discussed. The carina and tergum of P. imbricatus were considered 
by J. de C. Sowerby (1836, p. 340) to belong to his P. levis = 
P.ungus. The carina disagrees with that of P. unguis in being much 
narrower, straighter, more angular in transverse section, and in the 
presence of the well-marked grooves, which make a much more 
acute angle than do the growth-lines in P. wnguis. The tergum of 
P. imbricatus differs from that of P. wnguis mainly in having a much 
wider groove running parallel to the ocecludent margin, and about half 
the width of the occludent portion of the valve. The scutum of 
P. unguis differs in the general outline of the valve, which approaches 
an equilateral triangle, and consequently the apex is much more acute 
than in P. ¢mbricatus. The scutum of P. unguis is also much thicker, 
and has a deep pit for the adductor scutorum. 
There is little doubt that P. zmbricatus is closely allied to P. unguis, 
J. de C. Sowerby, and P. glaber, F. A. Roemer (1841, p. 104, pl. xvi, 
fig. 11). 
“The scutum of P. imbricatus is distinguished from all other scuta 
that I have seen, either of Pollicipes or Scalpellum, by the entire 
absence of any pit or depression for the adductor scutorum. 
Porticirres uneurs, J. de C. Sowerby. Figs. 4, 5. 
1836. Pollicipes unguwis, J. de C. Sowerby, Trans. Geol. Soc., ser. 11, vol. iv, p. 335, 
No Ser, 1a, B* 
1836, P. levis, J. de C. Sowerby, pag. cit., pl. xi, fig. 5. 
1845(?). P. ungwis, A. Reuss, Bohmischen Kreideformation, p. 17, pl. v, fig. 44. 
1850. P. wagwis, H. B. Geinitz, Das Quadersandsteingebirge, p. 100. 
1850. P. levis, H. B. Geinitz, ibid. 
TSI, 72h unguis, C. Darwin, Pal. Soc. Monogr. Foss. Lepadide, p. 64, pl. iv, fig. 1. 
1853. BP. unguis, C. Darwin, Ray Soc. Monogr. Sub-class Cirripedia, Synopsis et 
Index Systematicus, p. 637. 
1865. P. Megs. Salter & Woodward, Cat. and Chart. Foss. Crustacea, p. 27, pl. i 
fig. 
Uo 22 aan H. Woodward, B.M. Cat. Brit. Foss. Crustacea, p. 141. 
1886. P. unguis, J. Kafka, Sitz. Ber. k. Bohm. Gesell. Wiss. Sn Prag, 1885, p. 573. 
1887. P. wnguis, Fritsch & Kafka, Crust. Bohmischen Kreidef., p. 12. 
This common Gault species was founded by J. de C. Sowerby on 
a rostrum and one of the latera of the lower whorl. Darwin (1851, 
