ECHINODERMATA. 51 



with a straight bridge (fig. 1 c) ; the bevelled margins of the septa produce an appearance 

 like a third row of blind holes in the centre of the zone ; there are from thirteen to fourteen 

 pairs of pores opposite one of the large tubercular plates. 



The inter-ambulacral areas have a greater number of tubercular plates than is found in 

 any other Oolitic species ; in each column there are ten plates, the primary tubercles of 

 which are proportionately small; the areolas are oblong, and are rather deeply sunk, 

 with sharp, prominent margins ; the granules forming the scrobicular circle are not larger 

 than those filling the miliary zone ; the bosses are not very prominent, and are only a 

 little higher than the rim of the areolas ; their summits are flat, and sculptured with 

 fourteen deep crenulations (fig. 1 d) ; the tubercles are small in proportion to the dimen- 

 sions of the test, and are very uniform in size throughout the area ; the areolas on the 

 upper part of the areas are nearly circular, those at the under part are oblong ; only the 

 upper five areolas have complete circles of granules round their margins ; and the three or 

 four lower areolas are separated by a transverse ridge of the test, on which no granules 

 are developed. 



The miliary zone is broad and concave, and is filled with eight or nine rows of small 

 granules, set on eminences, around the bases of which circles of microscopic granules are 

 very regularly disposed ; between the poriferous zone and the adjoining row of tubercles, 

 there is a miliary zone filled with three or four rows of granules. 



The mouth opening is large (fig. 1 a) ; the peristome is pentagonal, but its figure 

 cannot be accurately described, as several of the plates are fractured ; the lantern is large, 

 and was composed of five powerful jaws, which remain with their teeth in situ. In the 

 fine specimen communicated by my friend, the Rev. P. B. Brodie, and figured in fig. 1 a, 

 each jaw consists of a broad central portion and two lateral carinse ; the long, curved, 

 conical, triangular teeth are bevelled into a chisel-like form on the inner surface, and 

 project five twentieths of an inch beyond the alveoli. 



The spines are long, slender, and tapering (PI. II, fig. 1 e, and PI. V, fig. 5 a, b, c, d, e) ; 

 the head is short, with a slightly prominent milled ring (fig. 5 c) ; the acetabulum is 

 sharply crenulated (fig. 5 d) ; the neck is marked, with fine longitudinal lines (fig. 5 c) ; 

 the stem is round or oval (fig. 5 e), and is covered with eight or nine prominent longitudi- 

 nal ridges, which have short, stout, oblique, forward-directed prickles developed from theii- 

 sm'face (fig. 5 a, c) ; a fragment of the stem (fig. 5 a) is nearly three inches in length. 



Affinities and differences. — This species very much resembles Cidaris Blumenbachii, 

 Mlinster, in the general structure of the test, but it is distinguished from that species by 

 the following characters : In Cidaris Blumenbachii the poriferous zones are narrow, and 

 the pores are all round ; the inter-ambulacra have only from six to seven tubercles in each 

 row, and the areolas are sunk and circular. In Cidaris Smithii the poriferous zones are 

 wide ; of each pair of pores, the one is round, and the other is oval j the inter-ambulacra 

 have ten tubercles in each row, and the areolas of the inferior tubercles are oval. Both 



