FROM THE UPPER CHALK. 143 



tubercles, eight in each, with large confluent areolae at the ambitus ; inter-ambulacra, two 

 rows of primary tubercles, nine to ten in each, with two short rows of small secondaries 

 at the base ; primary tubercles prominent at the ambitus, small and inconspicuous above ; 

 areolae large, radiated, and nearly confluent at the middle, very small above ; poriferous 

 zones undulated, unigeminal ; pores small. 



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

 inch. 



Description. — This beautiful little species occurs in the hard gritty Chalk of Dover. 

 The test is more highly ornamented than any of the preceding forms ; the tubercles at 

 the ambitus are highly developed, with radiated areolae, and nearly all of the same size. 

 On the upper surface they are proportionally small. The ambulacral segments slightly 

 project; this imparts a subpentagonal form to the body (fig. 2 a). There are two rows 

 of tut)ercles therein, eight in each, those at the ambitus being very large, and those on 

 the upper surface very small (fig. 2 c). The areolae of the large ambital tubercles are 

 confluent, and the smaller ones are separated from each other by a few granules 

 (fig. 2 c). 



The poriferous zones are narrow and much undulated (fig. 3 a) ; at the ambitus the 

 pores are small and unigeminal, and there are five pairs opposite each of the larger 

 plates. 



The inter-ambulacral areas are a little wider than the ambulacral, with two rows of 

 tubercles, nine to ten in each. The areolae are wide ; those at the ambitus and superior 

 surface have a radiated border at the circumference, the radii being formed of elongated 

 granules developed into a pyriform shape ; (fig. 3 b) represents four central plates 

 of an inter-arabulacral segment magnified eight times. In some of the plates small 

 miliary granules are introduced within the rayed circle. 



The discal opening is large, and of an elongated pentangular shape ; the angle cor- 

 responding to the single inter-ambulacrum projecting far down that segment (figs. 2 a 

 and b). 



Affinities and Differences. — This species in its general facies resembles C. spatuliferum, 

 but differs from it in having the tubercles on the upper surface disproportionately small 

 when compared with the large size they attain at the ambitus (figs. 2 3, c). This character 

 is very evident when fig. 2 c, PI. XXIX, is compared with fig. If, PI. XXVIII. The 

 radiated structure of the areolae is likewise another good diagnostic character between these 

 nearly allied forms. M. Cotteau appears to consider C. Wetherelli and C. spatdiferuin. 

 as varieties of C. striatum ; but, after a careful comparison of the specimens themselves 

 and with each other, 1 must dissent from this opinion. However much the tests of 

 Echinida per se may resemble one another, still we must not forget that the shell alone is 

 not the complete body of the animal, and that without its spines our evidence of specific 

 identity is incomplete : for example, the test of Ilemicidaris crenularis, Ag., is identical 

 with Hemicidaris intermedia, Flem. ; but the spines of the former are very different 



