FROM THE UPPER CHALK. 141 



unicura, we wait for the discovery of other specimens with spines before stating with 

 confidence its affinitive relations. 



Locality and Strati(/raphical Position. — Pound imbedded in a flint nodule at Gravesend, 

 from the Upper Chalk. The specimen belongs to the Museum of the Royal School of 

 Mines. 



Cyphosoma spatuliferum, Forbes,\^^Q. PI. XXVIII, figs. 1 a, b, c, d, e,f,g, h; PI. XXIX, 



figs. 1 a, b, c, d. 



Ctphosoma spatuliferum, Forbes. Dixon's Geology of Sussex, pi. xxiv, fig. 20, 



p. 340, 1850. 



— — Forbes. In Morris's Catalogue Brit. Foss., 2nd ed., 



p. 75, 1854. 



— — Woodward. Mem. Geol. Surv., Decade V, Supplement, 



p. 2, 1856. 



Test small, circular, inflated at the sides, concave at the base, and depressed on the 

 upper surface ; ambulacra prominent, two rows of tubercles, eight to ten in each j areolae 

 wide, bordered by granules ; inter-ambulacra with two rows of primary tubercles, nine 

 in each, and two short rows of secondary tubercles ; areolae wide, bordered by granules. 

 Poriferous zones much undulated ; pores unigeminal ; tubercles of both areas nearly 

 alike in size and structure. Mouth-opening one third the diameter of the test ; discal 

 aperture pentagonal, large and angular. Spines spatulate, very much flattened, smooth 

 except near the base, where there are fine longitudinal lines. 



Dimensions. — Height nine twentieths of an inch ; transiverse diameter seven tenths 

 of an inch. 



Description. — This beautiful little Cyphosoma has a circular body, with inflated sides 

 and small projecting equal-sized tubercles ; the ambulacral areas are prominent, and have 

 two rows of tubercles ; fig. 1/ shows one of these segments magnified six times ; the areolae 

 are wide, and fill nearly the entire plate ; the inner and upper margins of each are bor- 

 dered by a series of miliary granules, which define the boundary of the areolae, and entirely 

 prevent them becoming confluent. The tubercles at the ambitus are a little larger, and they 

 gradually become smaller as they approach the two apertures. The narrow poriferous 

 zones are much undulated, and form a series of crescents around the large plates ; there 

 are, in general, six pairs of holes opposite each plate, and they are entirely unigeminal 

 throughout (fig. 1/). 



The inter-arabulacral areas are a little wider than the ambulacral, and composed of large 

 plates (PI. XXVIII, fig. 1 g ; PL XXIX, fig. 1 d), of which there are nine in each column. 

 The areolas are wide, and bordered by a circle of miliary granules, complete on five sides 

 of the plate, but absent on lower margin (PL XXIX, fig. 1 d). The miliary zone is 



