GENEEA AND GEOUPS OF THE EGHINOIDEA. 105 



Ambulacra narrow, witli granules only in the interporiferous 

 areas, some having mamelons. Pairs of pores in low, broad 

 primary plates and in simple series abactinally and at the ambitus ; 

 actinally the series also persists, but there is a small demi-plate 

 intercalated close to the median ambulacral suture actinally to 

 large granules. This plate is sunken and has a pair of pores, 

 but probably is not in connexion with the ambulacro-interradial 

 suture, 



Interradia with two rows of vertically placed, large, crenulated, 

 imperforate tubercles, and no secondary tubercles. The trans- 

 verse sutures below the tubercles are deeply grooved, the base of 

 the tubercles being affected. 



Peristome subcircular, with branchial incisions ; the ambulacral 

 lips as large as those of the interradia. 



Fossil. Cretaceous : N. Africa, 



Grenus Tetgoistocidaeis, A. Agassiz, 1869, Bidl. Mus. Comp. 

 Zo'ol vol. i. ; 1872-74, Bevision, p, 289 ; 1881, ' Challenger ' 

 Beport, p. 111. 



Test small, thin, regularly arched above, circular in marginal 

 outline, depressed actinally. Epistroma moderate. 



Apical system ornamented or not, with very large basal plates, 

 excluding the radial plates from the elongate periproct, which is 

 covered by four plates, one being much the largest. 



Ambulacra with two principal vertical rows of plain primary 

 tubercles, united together by a reticulation of raised ornamen- 

 tation, producing the appearance of ridges and furrows ; pairs of 

 pores in straight series. 



Interradia with rows of plain tubercles slightly larger than 

 those of the ambulacra, and joined by the same kind of ornament ; 

 sutures of the plates either in the furrows between the ridges or 

 not visible ; small secondary tubercles may be amongst the variable 

 ornamentation. 



Peristome with slight branchial incisions, the actinal membrane 

 with ten buccal plates and others which imbricate. Spines 

 moderately long, slender, striated. 



Becent. Plorida, Caribbean Sea ; Josephine Bank ; Kermadec 

 Islands. 



The genus requires more careful working out, and from the 

 present knowledge of the species it should be classified with the 

 QlypJiocypJiince, but it has alliances with the Temnopleurince. 



