370 Mr. T. H. Withers on the 
Pollicipes glaber would in itself appear to be an extremely 
variable form, but whether the allied forms, occurring 
mainly in the upper zones of the Chalk, are really offshoots 
from that species, or whether they constitute closely-allied 
and parallel species, can be determined only by getting 
together a collection of properly-collected material from 
ditferent horizons. I have already gone some way in this 
direction, but the purport of this paper is not to discuss the 
species so much as to work out the structure of the capitulum, 
and to gain some idea as to the phylogenetic position of the 
group of species. 
Since most of the evidence is exhibited by the species 
Pollicipes unguis, we will now proceed to discuss the 
material, but it would seem unnecessary here to describe 
the valves of this species in detail, since this has already 
been done by Darwin, and myself in the case of the scutum. 
Scalpellum (Cretiscalpellum) unguis (J. de C. Sowerby). 
(Pl. V. figs. 1-10.) 
1836, Pollicipes unguis, J. de C. Sowerby, Trans. Geol. Soc. ser. 2, 
vol. iv. p. 339, pl. xi. fig. 5*. 
1886. Pollicipes levis, J. de C. Sowerby, zdzd. pl. xi. fig. 5 (non 
pl. xvi. fig. 1). 
1845. Non Pollicipes unguis, J. de C. Sowerby; A. Reuss, Béhm. 
Kreidef. p. 17, pl. v. fig. 44. 7 
1850. Pollicipes unguis, J. de C. Sowerby; H. B. Geinitz, Das 
Quadersandsteingeb. p. 100. 
1850. Pollicipes levis, J. de C. Sowerby; H. B. Geinitz, did. p. 100. 
1351. Pollicipes ungurs, J. de C. Sowerby; C. Darwin, Pal. Soc. 
Monogr. Foss. Lepadide, p. 64, pl. iv. fig. 1. 
1854. Pollicipes unguis, J. de ©. Sowerby; C. Darwin, Ray Soe. 
Monogr. Subclass Cirripedia, Synop. et Index Systematicus, 
p. 637. 
1854. Pollicipes unguis, J. de C. Sowerby; J. Morris, Cat. Brit. Foss. 
2nd ed. p. 96. 
1865. Pollicipes unguis, J. de C. Sowerby ; Salter and H. Woodward, 
Cat. & Chart Foss. Crustacea, p. 27, pl. i. fig. 6. 
1877. Pollicipes unguis, J. de C. Sowerby ; H. Woodward, Brit. Mus. 
Cat. Brit. Foss. Crustacea, p. 141. 
1886. Non Pollictpes unguis, J. de C. Sowerby; J. Kafka, Sitz. Ber. k. 
Bohm. Gesell. Wiss. Prag (1885), p. 573 (=P. glaber, Roemer). 
1887. Non Pollicipes unguis, J. de C. Sowerby; Fritsch and Kafka, 
Crust. Bohmischen Kreidef. p. 12 (=P. glaber, Roemer). 
1910. Pollicipes unguis, J. de C. Sowerby ; Withers, Geol, Mag. dec. v. 
vol. vil. p. 498, text-figs. 4, 5a, d. 
Diagnosis —Carina bowed inwards, comparatively wide at 
the base, and the basal margin bluntly pointed and usually 
somewhat rounded ; rostrum subtriangular, bowed inwards, 
and transversely convex; carinal latus with the upper and 
ies 
