370 Mr. T. H. Witliers on the 



PoUicipes glaber would in itself appear to be an extremely 

 variable form, but whether the allied forms, occurriii;^ 

 mainly in the upper zones of the Chalk, are really ort'shoots 

 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 

 ditierent 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 phylogeuetic position of the 

 group of species. 



Since most of the evidence is exhibited by the species 

 PoUicipes unt/uis, 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. Sowerbv). 

 (PI. V. figs. 1-10.) 



1836. PoUicipes unguis, J. de C. Sowerby, Trans. Geol. Soc. sor. 2, 



vol. iv. p. y3o, pi. xi. fig. 6*. 

 1836. PoUicipes Icevis, J. de C. Sowerby, ibid. pi. xi. fig. 5 (non 



pi. xvi. tig. 1). 

 1845. Non PoUicipes unguis, J. de C. Sowerby; A. Reuss, Biihrn. 



Kreidef. p. 17, pi. v. fig. 44. 

 1850. PoUicipes unguis, J. de C. Sowerby ; H. B. Geinitz, Das 



Quadersandsteingeb. p. 100. 

 1850. PoUicipes Icevis, J. de C. Sowerby; H. B. Geinitz, ibid. p. 100. 

 Idol. PoUicipes unguis, J. de C. Sowerby ; C. Darwin, Pal. Soc. 



Monogr. Foss. Lepadida), p. 64, pi. iv. fig. 1. 

 1854. PoUicipes unguis, J. de 0, Sowerby ; C. Darwin, Ray Soc. 



Monogr. Subclass Cirripedia, Synop. et Index Systematicus, 



p. 637. 

 1854. PoUicipes unguis, J. de C. Sowerby ; J. Moms, Cat. Brit. Foss. 



2nd ed. p. 96. 

 18G5. PoUicipes wiguis, J. de C. Sowerby ; Salter and H. Woodward, 



Cat. & Chart Foss. Crustacea, p. 27, pi. i. fig. 6, 

 1877. PoUicipes unguis, J. de C. Sowerby; H. Woodsvard, Brit. Mus. 



Cat. Brit. Foss. Crustacea, p. 141.- 



1886. Non PoUicipes unguis, J. de C. Sowerby; J. Kafka, Sitz. Ber. k. 



B5hm. Gesell. Wiss. Prag (1885), p. 5^3 { = P. glaber, Koeraer). 



1887. Non PoUicipes unguis, J. de C. Sowerby ; Fritsch and Kafka, 



Crust. Bohniischeu Kreidef. p. 12 ( = P. glaber, lloenier). 

 1910. PoUicipes unguis, J. de C. Sowerby ; Withers, Geol. Mag. dec. v. 

 vol. vii. p. 498, text-figs. 4, 6a, b. 



Diagnosis. — Carina bowed inwards, comparatively wide at 

 the base, and the basal margin bluntly pointed and usually 

 somewhat rounded ; rostrum siil)triangular, bowed inwards, 

 and transversely convex ; carinul latus with tJ)e upper and 



