CLARK: THE ECHINODERMS OF PERU. 353 



coasts of Peru. It reaches a length of 55 mm., and iii life is sulphur-yellow in 

 color. It lives among mussel-shells (Mytilus) and stones in shallow water along 

 shore. 



Colochirus peruanus. 



C. Semper, 1868. Reisen im Arch. d. Phil., 2 Th., 1, 5 heft, p. 239. 



As this species has not been met with since it was described by Semper, there 

 is nothing further to be recorded of it, save that the specimens he had were "yel- 

 lowish," 15-18 mm. long and 6-7 mm. in diameter. They were recorded as from 

 Peru, but whether it was Peru, South America, or Peru, Gilbert Islands, remains 

 to be shown. 



Thyone gibber. 



Stolus gibber E. Selenka, 1867. Zeit. f. w. Zool., 17, p. .356. 



Thyone gibber C. Semper, 1868. Reisen im Arch. d. Phil., 2 Th., 1, 2 heft, p. 66. 



Plate 14, figures 3-6. 



Selenka's description is very brief and he gives no figures, so that a detailed 

 descri-ption and a few figures are desirable, especially as the species does not 

 seem to have been met with since it was described; it is entirely overlooked 

 by Lampert (1885) and omitted from his monograph. The following are the 

 chief characters : — 



I'eutacles 10, of which the two ventral are very small. Pedicels very numer- 

 ous, covering all parts of the body. Body wall firm and leathery. Calcareous 

 ring well developed (fig. 2) ; radial pieces much larger than interradial and with 

 conspicuous posterior prolongations. Polian vessels 3, of which one is very 

 small. Stone-canal single, iu the dorsal mesentery ; madreporic body elongate, 

 cylindrical, truncate at end and somewhat convolute or spirally wound. Repro- 

 ductive organs situated posterior to the middle of the body,, consisting of a tuft 

 of yellowish, unbrauched tubules on each side of the mesentery. Alimentary 

 canal and respiratory-trees apparently not peculiar. Anus without calcareous 

 teeth. Calcareous deposits in body wall abundant, in the form of kuobbed, per- 

 forated buttons (figs. 3, i) about .09 mm. long ; while there is more or less 

 diversity in details and some are not perfectly formed, most of the buttons have 

 4: large perforations, 10 knobs on the margin (on each surface) and 2 cousj^icuous, 

 elevated knobs, connected by a thick ridge, iu the middle of each surface. There 

 seem to be no other deposits in the body wall. In the pedicels, besides terminal 

 discs, we find that the buttons become elongated into curved supporting rods 

 (figs. 5, 6), without knobs on the margin but flattened and perforated at the 

 ends ; the knobs at the middle of the plate disappear on the concaA'e surface, but 

 remain as more or less conspicuous elevations on the convex side. The tentacles 

 are literally packed full of perforated supporting plates and rods ; in the tips of 

 the branches these are small and comparable with those in the pedicels, but in the 

 main trunk and its branches they are much larger and are more like elongated 



