HOLOTHURIOIDEA, ASTEROIDEA, AND ECHINOIDEA 389 



III. Echinoidea 



by 

 TH. MORTENSEN. 



The collection of Echinoidea, brought home from Juan Fernandez by 

 Mr. Backstrom, unfortunately only contains one single species Nacospaiangns 

 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. Abatiis 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. de Pourtales. Zoological Results of the Hassler Expedition. 



I. Echini, Crinoids and Corals. 111. Cat. Mus. Comp. Zool. VIII. 1874. 



p. 18. PI. II. Figs. 3-5. 

 A. Agassiz. The Panamic Deep Sea Echini. Mem. Mus. Comp. Zool. XXXI. 



1904. p. 202; PI. 98. 

 H. L. Clark. Hawaiian and other Pacific Echini. The Echinoneidae . . . and 



Spatangidse. Mem. Mus. Comp. Zool. XLVI. 191 7, p. 149. PI. 145. Figs. 



35—39- 



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 algae, 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 PI. 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 PI. 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 



^ Th. Mortensen: The Echinoidea of the Swedish South Polar Expedition. Wiss. Er- 

 gebn. d. Schwed. Siidp. Exp. 1901 — 1903. Bd. VI. 4. 1910 (p. 74). 



