150 



PELTASTES. 



A. 



Species from the Lower Greensand or Neocomian. 



Peltastes Wrightii, Desor. PI. XXX, fig. 1 a—f, fig. 2. 



Salenia punctata, Forbes. In Morris' Catalogue of British Fossils, 2ncl ed., 



p. 89, 1854. 

 — — Woodward, Memoirs of Geol. Surv., App. to Decade V, 



p. 7, 1856. 

 Hyposalenia Wrightii, Besor. Synopsis des Echinides fossiles, p. 148, 1856. 

 Peltastes — Cotteau. Paleontologie Fran9aise ; Terrain Cretace, tome 



vii, pi. 1028, figs. 1—7. 



Diagnosis. — Test circular, upper surface convex, sides inflated, under surface flat, 

 ambulacra narrow, slightly flexuous, with two rows of granules fifteen in each, equal in 

 size, and mammillated ; poriferous zones slightly flexed, pores unigemmal, set in oblique 

 pairs, and multiplied around the peristome ; inter-ambulacra wide, with five or six large 

 prominent tubercles, increasing in size from the peristome upwards. Apical disc very 

 large, convex, subcircular, plates smooth, sutures marked with isolated points, periprocte 

 transversely oblong, a little prominent; mouth-opening large, peristome divided by 

 feeble indentations into ten lobes. 



Dimensions. — Height six tenths of an inch ; transverse diameter one inch. 



Description. — This beautiful typical form of Peltastes, and the oldest we at present 

 know, appears in our lists of English fossils as 8alenia punctata, one of the synonyms of 

 Peltastes stellulatus. A comparative study of specimens, however, convinced M. Desor 

 that the identification was erroneous ; and he described^ our Farringdon urchin as a well- 

 marked and distinct species, resembling Peltastes stellulatus, but separated from it in 

 having a more inflated test, with more numerous and less prominent tubercles, the apical 

 disc thinner and smoother, and marked only with some isolated punctations. 



The test is circular, the sides are a little inflated, and the upper surface is convex and 

 depressed ; the ambulacral areas are narrow and very slightly flexed with two rows of 

 mammillated granules, about fifteen in each. They are very uniform in size and arrange- 

 ment throughout the area, except at the base, where two pairs are a little larger ; a line 

 ■of microscopic granules down the middle of the area divides the larger lateral rows from 

 each other (PI. XXX, fig. 1 e). The poriferous zones are wide for so small a test, and 

 the pairs of pores are obliquely but very regularly arranged in a unigerainal series ; near 

 the peristome, however, they become a little more crowded and doubled. 



The inter-ambulacral areas are wide, and in the large specimen I have figured fig. ] a 



1 i 



Synopsis des Echinides fossiles,' p. 148. 



