208 PROCEEDINGS OF THE AMEEICAN ACADEMY 



nus, as well as Homolampas and Palaeotropus, with the actinostome 

 nearly in one plane, form a ready transition to the actinostome of the 

 Nucleolidse and Echinolampadae by the additional development of the 

 interambulacral tubercles in immediate proximity to the actinostome 

 and their crowding together to form bourrelets more or less prominent, 

 and thus pass into such types as Neolampas, which have the simple 

 ambulacra of this group, with the actinostome of the Echinolampadaa 

 proper. 



Cystechinus Wyvillii, A. Ag., nov. sp. 



The outline of test seen from above is nearly elliptical, slightly 

 broader anteriorly across the actinostome. Seen endwise, the outline 

 is conical, with rounded apex and sides gradually rounding to ambitus. 

 Actinal surface flat, slightly sunken actinostome, anal system near pos- 

 terior edge on actinal side. Seen in profile, the outline is also conical, 

 with rounded apex placed slightly posteriorly (apex and apical system 

 coincide). The test slopes, with slightly re-entering sides towards 

 the anterior and posterior extremities, passing into ambitus with a 

 rather abruptly rounded outline near edge of test. The whole test is 

 covered with short, sharp spines, carried by the few large tubercles 

 arranged on the primary plates. Ridges radiating from the centre of 

 each plate give to the side of the test, when denuded, a peculiarly 

 ornate appearance. The color of the test is violet, spines of same 

 color, darker. 'Test quite thin and very variable in outline according 

 to age. Young specimens are quite flat. — Station 14G, 1,375 fathoms; 

 Station 147, 1,600 fathoms; Station 158, 1,800 fathoms. 



Cystechinus clypeatus, A. Ag., nov. sp. 



Judging from the fragments of the test of this species, it must have 

 grown to a very large size, probably five or six inches in diameter. 

 It differs from the preceding species in having a much shorter test ; 

 the arrangement of the plates of the anal system is quite different in 

 this and the preceding species. In C. clypeatus, although the speci- 

 mens are larger, there are fewer plates covering the anal system than 

 in C. Wyvillii; in this species the genital plates are also much larger 

 in proportion. Judging from a fragment of the actinostome, the 

 actinal surface was more closely covered with primary tubercles than 

 in the preceding species. — Station 133, 1,900 fathoms ; Station 205, 

 1,050 fathoms. 



