HOLOTHURIOIDEA, ASTEROIDEA, AND ECHINOIDEA 389 
lll. Echinoidea 
by 
TH. MORTENSEN. 
The collection of Echinoidea, brought home from Juan Fernandez by 
Mr. BACKSTROM, unfortunately only contains one single species Nacospatangus 
gracilis A. Ag., in two specimens. It is obvious that this is not a fair repre- 
sentation of the Echinoid fauna of Juan Fernandez. At least one more species 
is known to occur there, viz. Adatus cavernosus (Phil.)', but there can hardly 
be any doubt that several more of the Echinoids of the Magellanic region will 
prove to occur there. It is, therefore, not appropriate to discuss the zoogeo- 
graphical questions on the base of the insufficiently explored Echinoid fauna 
of this island. 
Nacospatangus gracilis A. Ag. 
Literature. 
A. AGassiz and F. pe PourtatEs. Zoological Results of the Hassler Expedition. 
I. Echini, Crinoids and Corals. Ill. Cat. Mus. Comp. Zool. VIII. 1874. 
mo.) 2. Bigs; 4s: 
A. Acassiz. The Panamic Deep Sea Echini. Mem. Mus. Comp. Zool. XXXI. 
fao4. p..202: Pl.-98. 
H. L. Crarkx. Hawaiian and other Pacific Echini. The Echinoneide... and 
Spatangide. Mem. Mus. Comp. Zool. XLVI. 1917, p. 149. Pl. 145. Figs. 
a5. oo: 
Two specimens of 24 mm. and 8 mm. length, both more or less broken, 
dredged in a depth of 30—45 metres on a bottom with calcareous alge, off 
Masafuera, Juan Fernandez. (K. BACKSTROM.) 
The species is so well known that very little additional information can 
be given; only the apical system and the pedicellariae require some few 
remarks. 
The apical system of the adult has not been represented or described in 
detail, but the outlines of the plates are clearly seen in Pl. 98, fig. 3 of the 
»Panamic Deep Sea Echini»; the madreporic plate is seen to be devided in an 
anterior and a posterior part, the latter alone being provided with madreporic 
pores. I find the pores to occur both in the anterior and the posterior part. 
Also I find the shape of the plates and the position of the large genital pores 
somewhat different from that shown in the figure referred to above. (Comp. 
fig. 3.) In the younger specimen I likewise find the apical plates rather dif- 
ferent from the representation, given in Pl. 98, fig. 5 of the »Panamic Deep Sea 
Echini> from a specimen 6,5 mm. length (comp. fig. 4). It is evident that the 
differences between the two figures are not due to the difference in size; the 
1 Tu. MorTENSEN: The Echinoidea of the Swedish South Polar Expedition. Wiss. Er- 
gebn. d. Schwed. Sidp. Exp. 1901—1903. Bd. VI. 4. 1910 (p. 74). 
