142 CYPHOSOMA 



narrow at the ambitus, where it is crowded with granules, and wide at the upper sur- 

 face, where it is depressed and nearly nude (PI. XXVIII, fig. Id). At the base of the 

 area, between the primary tubercles and the poriferous zones, there is a short row of small 

 secondary tubercles (fig. 1 c), which extends from the peristome to the ambitus; fig. 1 /i 

 shows the base of this segment magnified six times; the small secondaries are raised 

 upon bosses (fig. 1 /i). 



The tubercles of both areas are nearly of the same size ; the boss is large, with feeble 

 crenulations, closely embracing the mammillon, Avhichis very prominent (PI. XXIX,fig. 1 d). 



The base is concave, and the mouth-opening, one third the diameter of the test, is in 

 a slight depression (fig. 1 c). The peristome is divided by slight incisions into ten nearly 

 equal-sized lobes. The discal opening is large and pentagonal. The mould of the single 

 ovarial plate descends further into the segment than either the antero- or postero- 

 lateral ovarials into their respective areas. 



The spines of this Urchin are spatulate, and the stem is extremely smooth, except near 

 the milled ring, where the base is marked by fine longitudinal hues. 



Affinities and Differences. — The spatulate form of the spines distinguish this 

 species from C. coroUare, with which it has many affinities in the anatomy of the test ; 

 C. spatuliferum is, however, a smaller Urchin, more compressed and pentagonal, less 

 inflated at the sides, and more depressed on the upper side than C. coroUare ; the surface 

 of the test is, likewise, rougher in consequence of the numerous small tubercles that 

 project sharply from the plates. 



Locality and Stratigrajjhical Position. — This is a rare species in the Upper Chalk of 

 Kent and Sussex. The type specimens of the Dixon Collection are now in the British 

 Museum. One of these I have figured in PI. XXVIII, fig. 1 ; and a still larger specimen, 

 from the Rev. T. Wiltshire's Cabinet, in PI. XXIX, fig. 1. 



CypHOSOMA RADiATUM, Sori(jnet, 1850. PI. XXIX, figs. 2 a, b, c ; figs. 3 a, b. 



CrPHOsoMA ? (small or young), Dixon. Geol. Sussex, p. x, pi. xxiv, figs. 28 — 31, 1850. 



— RADIATUM, Sorignet. bursins foss. du Dep. de I'Eure, p. 28, 1850. 



— SIMPLEX, i^orif*. Morris's Catalogue of Brit. Foss., p. 74, 1854. 



- — — Woodward. Mem. Geol. Surv., Decade V, App., p. 1, 1856. 



Phtmosoma Heberti, Besor. Synopsis des Echinides foss.. Supplement, p. 450, 



1858. 

 CyPHOSOMA PERFECTUM, Cotteau tt Triger (pars). Echinides du Depart, de la Sarthe, 



p. 375, 1862. 

 Phtmosoma Heberti, Dvjardin et Hupe. Hist. Nat. des Echinoderm., p. 508, 1862. 



— SIMPLEX, Dujardin et HupL Ibid. 



Ctphosoma r.\diatum, Cotteau. ^Paleontologie Fran^nise ; Ter. Cret., pi. 11-1", fio-s. 



10—14; pi. 1148, p. 609, 1864. 



Test small, subpentagonal, convex above, base concave; ambulacra, two rows of 



