744 SUMMARY OF CUBKENT RESEARCHES RELATING TO 



been described by earlier or later authors under other names, with the 

 excei^tion of one (A. Mertensi) among these seventeen, which has been 

 insufl&ciently characterized. The sj^ecies that are held good are — 

 Cucumaria albida, C. nigricans, Stichopus chloronotus, S. sitchaensis, 

 Eolothuria sordida, and H. tigris. The synonymy of the different 

 species is amply dealt with, and some remarks are made on each of 

 them. 



Observations on the Echinoidea.* — Prof. F. Jeffrey Bell in his 

 fourth part deals especially with the Echinometridfe, their affinities 

 and systematic position. He points out that the discoveries of late 

 years make it now easier to propose a scheme of classification of the 

 regular Echinoidea. Adopting the divisions suggested by Ludwig, 

 which depend on the possession or absence of external gills, and 

 recognizing the significance of Echinothnria, to which, as possessing 

 more than one pair of each series of ambulacral plates carried on 

 to the buccal membrane he applies the term polylepid, he distin- 

 guishes the rest of the branchiate Echinoids as decalepid, as, in them, 

 only five pairs of ambulacral plates are found on the buccal mem- 

 brane. Of these the Salenidse are palceoproctous, while the rest are 

 neojyroctous ; among the latter some of the primary pore-plates 

 always lose their primitive relations ; but in the Arbaciadae and Dia- 

 dematidse this does not always affect the plates above the ambitus, 

 and the poriferous zones are in both almost straight ; they are 

 palceosticha, as compared with the Echinidae and Echinometridae, 

 which are neosticha. 



These relations are exhibited in the subjoined table : 



" No external gills. Auricular arch not complete and not 

 radial. Ambulacral and interambulacral plates continued on to 

 buccal membrane ; pores in straight rows, all the pore-plates 

 primary and subequal. Entobkanchiata. 



Fam. 1. CidaridcB. 



External gills, auricles radial ; interambulacral plates not con- 

 tinued on to the buccal membrane. Ectobrajs'chiata. 



Series a. (Palseoproctous.) 



Large suranal plate persistent in apical area. 



Fam. 2. Salenidce. 



Series yS. (Neoproctous.) 

 Anal plates all secondary. 



Subseries i. (polylepid). 



More than one pair of ambulacral plates carried on to the buccal 

 membrane from each area. Fam. 3. Echinothuridce. 



Subseries ii. (decalepid). 

 Only five pairs of ambulacral plates on the buccal membrane. 



* Proc. Zool. Soc, 1881, pp. 410-33 (2 figs.). 



