FROM THE GAULT. 95 



arabulacral areas are wide and have two rows of tubercles ; those on the lower portion of 

 the area are large and closely set together, and those on the upper part are dispropor- 

 tionately small and placed widely apart (fig. 1 b) ; some very fine granules divide the large 

 basal tubercles, and a numerous granulation surrounds the smaller tubercles on the upper 

 part (fig. 1 b). 



The inter-ambulacral areas possess only two rows of primary tubercles ; those near the 

 base are about the same size as the corresponding tubercles in the ambulacra, on the upper 

 part of the area, they are larger, and diminish more gradually in size, so that the 

 difference in the tubercles on the upper surface readily distinguishes the ambulacral from 

 the inter-ambulacral areas ; an irregular row of four small secondary tubercles occupies 

 the outer side of the base between the primaries and the poriferous zones, and a like 

 central row extends through the middle of the lower part thereof (fig. 1 c). 



The miliary zone is wide and depressed in the upper part, and the plates are here 

 covered with numerous small granules, that cluster chiefly around the bases of the small 

 tubercles, the median sutural space being depressed and nude (fig. 1 b) ; the lower part 

 of the zone is narrow, and the granules are much larger and more closely set together ; 

 many of them are raised on small mammillons, with secondary tubercles interspersed 

 among them (fig. 1 c). 



The large primary tubercles of both areas have very large areolas (fig. 1, c), with well 

 defined margins. Each areola consists of two parts, an outer circle, consisting of a band 

 covered with microscopic granules (fig. 1 d), and a smooth inner portion, from whence the 

 boss arises (fig. 1 e). This kind of ornamention is very remarkable ; it is very well pre- 

 served in the fragment before me, and correctly represented in figs, d and e. The summit 

 of the boss is sharply crenulated, and the tubercle deeply perforated. 



The spines were long and slender, as seen by some imprints on the slab (figs. 1, 2, 3) ; 

 the acetabulum of the small head is marked by coarse crenulations, the milled ring is 

 prominent, and the whole surface of the stem covered with fine longitudinal lines. 



Affinities and Differences. — This species belongs to the group of which P. NormanicB 

 (PI. XXI, fig. 3) may be regarded as the type. It difiers from that species, however, in 

 having smaller primary tubercles and fewer and smaller secondaries, in having narrower 

 ambulacra and less flexuous poriferous zones. The miliary zone is likewise less distinctly 

 marked ; the general contour of the test is diflferent, for the upper and lower surfaces are 

 more depressed and the sides less inflated. 



Locality and Stratigrapldcal Position. — This unique specimen was found by the Rev. 

 T. Wiltshire, F.G.S., in the Gault at Folkestone, in a bed near the base of that formation. 

 I have very great pleasure in dedicating this species to my kind friend as an acknow- 

 ledgment of the important assistance he has rendered me during the progress of this 

 work, by the generous contribution of all his best specimens for figuring, his able notes 

 on certain species of Cidaris, and other valuable aid frankly given on all occasions when 

 required. 



