Bd. VI: 4) 
THE ECHINOIDEA. 
77 
been separately acquired by the Salenids and Echinids proper, which leads to the 
conclusion that the alleged homology between this plate and the dorsocentral plate 
of the Crinoids is false. LovÉn’s suggestion, that the small plates on the periproct 
are »the rudiments of the central ossicle and the costal 5» (On Pourtalesia p. 74. 
PL XIV. Fig. 164), seems unacceptable, resting, in fact, on no evidence at all, only 
on the a priori assumption that the central plate must be represented in some way. 
(Regarding the »costal» 5 see below). Still less acceptable appears his explanation 
of the madreporite of the Ethmolytic Spatangoids as being composed of genital 
(costal) 2, the central plate and genital (costal) 5 (On Pourtalesia p. 71). The exi- 
stence of a separate genital 5 proves that the madreporite has not absorbed this 
plate, as it were; it has, upon the whole, nothing to do with this plate. Unfor- 
tunately, I am unable to state beyond doubt the ultimate fate of genital 5. There 
are only two alternatives, viz. that it may be resorbed and disappear totally, or that 
it may remain as the posterior of the periproctal plates. I think the latter alter- 
native is the more probable, but I cannot give definite proof for it. 
Fig. 16. Apical area of Abattis cavernosus. l, 9 mm. 
Simplified copy of PI. XVII. Fig. 9. The genitals 
are numbered 1, 2, 3 etc., the oculars I, II, III etc. 
5 
Fig. 15. Copy of the figure 308 of A. Agassiz’ 
»Panamic Deep Sea Echini», representing the apical 
area of Abattis cavernosus , ( contains ) 1,9 mm. 
A corresponding stage of the development of Abatus cordatus has been figured 
by LovÉN (On Pourtalesia. PI. XIV) and by A. AGASSIZ (Panamic Deep Sea Echini 
PI. 99. Figs. I — 7, p. 2 T 3, figures 307 — 308) (under the name of Abatus cavernosas). 
While the explanation of the apical plates given by LovÉN (Op. cit. PL XIV. Fig. 
164 a) is evidently correct, as far as he has been able to trace the plates, the ex- 
planation of these plates given by AGASSIZ is evidently unacceptable, as is easily 
seen on comparing the figures 15 and 16, the former representing the figure 308 
from the »Panamic Deep Sea Echini», the latter a simplified copy of the PL XVII. 
