258 PEor. p. M. Duncan's eetision of the 



anterior basal, centrally and posteriorly, so as to separate tlie 

 postero-lateral basal plates and the posterior radial plates, and 

 extend into the posterior interradinm. 



Ambulacra dissimilar, the anterior in a faint groove, with small 

 pairs of round pores ; the paired ambulacra semipetaloid, flush, 

 all open distally, the antero-lateral widely divergent dorsally, and 

 the postero-lateral with broad smooth plates on either side of 

 the amphisteruum ; the pores of the semipetaloid parts round, 

 but the outer pore of the pairs may be slightly elongate ; pores 

 single and distant below the semipetaloid parts, and some with 

 peripodia around the peristome. 



Peristome excentric in front, in a moderate concavity of the 

 test, much broader than long, semi-lunar with rounded ends. 

 Posterior labrum broad, projecting. Sternum with a more or 

 less defined keel (amphisternous). Periproct supramarginal, 

 circular, much plated. 



Ornamentation of few or numerous small primary tubercles 

 on each plate abactinally, edges and sutures of plates more or less- 

 plain ; miliaries between the tubercles. Actinally the tubercles 

 are subequal and more crowded, and most numerous within 

 and around the subanal fasciole. Primary spines long or short, 

 slender, curved, smallest actinally. Pedicellarise long ; the tri- 

 dactyle forms with slender valves. Ambulacra with much smaller 

 tubercles beyond the subpetaloid part than in the interradia. 



A narrow peripetalous fasciole passing above the periproct ; a 

 subanal fasciole, broad or narrow heart-shaped, partly in contact 

 with the actinal edge of the periproct. 



Recent. Caribbean Sea, 38 to 298 fathoms ; Japan and the 

 Philippine Islands, 345 to 375 fathoms. 



The species which is found in the deepest water has the 

 shorte&t spines and the ambulacra the most apetaloid. 



Grenus ISTeopneustes, gen. nov. 



Syn. Bhinolrissus, A. Agassiz, 1883, 'Blake' Echini, p. 67, 

 pis. 23 &2G (pars). 



Test moderate in size, thin, ovoid in outline at the margin, 

 longer than broad and broader than high ; tumid abactinally, at 

 the sides ; low, broadest and tumid anteriorly, highest and trun- 

 cated posteriorly; with a backward and downward projecting 

 actinal plastron. Anterior groove absent. 



