282 ECHINOSPATAGUS 



they differed from each other considerably in form, and in degree of depth of the dorsal 

 ambulacra and the number of the pores in the zones. 



A. 



Length l^s 



Breadth l^ 



Height 1^^ 



Anterior single ambulacrum . . .28 pairs 

 Antero-lateral pair „ ... 43 pairs 



Postero-lateral pair „ ... 20 



The anteal sulcus in which the single ambulacrum is lodged is deep, wide, finely 

 granulated and tuberculated. The pairs of pores are arranged on the sides of the area in 

 single files, and the pores forming a pair are separated from each other by distinct 

 tubercles. 



The antero-lateral pair are doubly flexed, and the postero-lateral pair, slightly bent, are 

 about half their length. The floors of all the areas arc nearly smooth, and the pores, with 

 their small transverse slits in the zones, are set at short distances apart. The portions of 

 the test between the petals form obtuse eminences near the apical disc, that body reposing 

 at the confluence of the five valleys. On these inter-ambulacral elevations the tubercles 

 are more numerous and set closer together than on other portions of the upper surface, 

 fig. 1 a and fig. 1 c. 



The apical disc is small, and composed of four perforated, ovarial plates ; the right 

 antei'o-lateral is the largest, and supports the madreporiform tubercle on its surface. The 

 five ocular plates are very small, fig. 1 //. 



The surface of the plates is finely granulated, among which there are developed many 

 well-formed tubercles ; these become more numerous on the sides, they increase in size 

 and number at the ambitus, and are large and set closely together at the base, on the 

 plastron of which they are very conspicuous, fig. 1 d. 



Mr. Bone copied fig. 1, PI. LX, from Decade V, pi. ix, ' Memoirs of the Geol. Survey.' 

 In this figure, drawn under the direction of Professor Forbes, a portion of the surface 

 adjoining the right postero-lateral ambulacrum was magnified to show the diffused 

 condition of the fasciole. As I have carefully examined many very good tests of this 

 species without observing such a structure, I am convinced that a mistake was committed, 

 which my friend unfortunately imported into PI. LX, fig. 1 /, of this work, as no true 

 fasciole exists in this species. 



The base is flat or rounded, and the peristome situated at the anterior fourth of the 

 under surface ; the tubercles on this region are very large, they are raised upon crenulated 

 bosses, and their summits are perforated; the areola is surrounded by a chain of 

 granules, which completely incircle the areolar boundaries (fig. 1 i). 



Affinities and Bifferences. — This Urchin is well characterised by its large and deep 

 anteal sulcus, its bi-flexed antero-lateral ambulacra, the small postero-lateral pair, and 



