GENEEA ATSTD GROUPS OF THE ECHINOIDEA. 223 



the pores close, and the outer row the largest ; the postero-lateral 

 continued over the margin actinally as very broad areas, which 

 nearly join and pass forwards ou either side of a very linear 

 sternum ; the antero-lateral with some doubling of pairs near 

 the peristome. 



Ornamentation of the interradia of secondary tubercles and 

 miliaries, largest near the ambitus, and actinally there are larger 

 tubercles, which are more distant, and also miliaries. 



Peristome large, semicircular, excentric in front, slightly 

 sunken, with a feeble labrum, so that the margins are on the 

 same level. Posterior interradium actinally with an ill-developed 

 narrow sternum, which becomes a small triangular surface behind 

 the close ambulacral areas. Periproct poiuted, elliptical, marginal. 

 Pascioles absent. 



Recent. Position unknown. 



The genus Palceopneustes, A. Agassiz, is one of the most in- 

 teresting of the series described by its distinguished founder ; it 

 gave him much trouble, and he has pointed out how strange are 

 its superficial and positive alliances with Cretaceous, Tertiary, 

 and recent types. The difS.culty of grasping the true meaning 

 of the genus has, in consequence of the association of Lino- 

 pneustes with it as a subgenus, been increased, and it appears 

 really straining a point to classify so closely forms with and 

 without well-developed marginal and subanal fascioles. It is 

 proposed to raise Linopneustes (p. 258) to the position of a genus. 



Genus Pal^opneustes, A. Agassiz, 1873, Bull. Mus. Gomp. Zo'ol. 

 Sarv. iii. no. 8, p. 188 ; 1874, Hassler Exped. Ech., Mem. 

 Mus. Gomp- Zo'ol. Harv. no. viii. p. 13 ; 1883, Beport on the 

 '•Blake'' Ech., op.cit. no. x. p. 60. {Modified.) 



Test large, with a sharply defined or somewhat tumid ovoid 

 ambitus, moderately high, subcorneal or subhemispherical abacti- 

 nally, broadest anteriorly, broader than high ; actinally flat, with 

 a posterior oblique truncation. 



Apical system slightly excentric in front, small, with four 

 basal plates, three or all perforated, the right anterior containing 

 part of the madreporite, which extends beyond, centrally, and 

 separates the postero-lateral basal plates and also the posterior 

 radial plates, and passes slightly into the posterior interradium. 



