124 NATURAL HISTORY BULLETIN 



Pectinate pedicellariae may be present on the interactinal 

 plates, or between tliem, or on the inner end of the inferomar- 

 ginal plates, or sometimes on the adambulacrals. They may be 

 few or many, or entirely lacking, especially in the young. 



Ludwig (op. cit., 1910) made the external generic distinction 

 between this genus and Luidiaster almost entirely dependent on 

 the presence of one spine, in this, on the actinal side of the adam- 

 bulacral plate, while in Luidiaster there are two or more. This, 

 however, is not a valid generic difference, for several of the 

 species have either one or two, on consecutive plates, and nearly 

 all have two, in large specimens, on some of the plates. 



The internal dorsal muscular bands of the rays are not at- 

 tached to a crest of the proximal ambulacra! ossicles, in those 

 species examined. According to Fisher, this is the most definite 

 character for separating it from Luidiaster. The same charac- 

 ter seems to separate it from Pectinuster. But the muscular 

 bands are not known in many species. Dry specimens and 

 unique types cannot be examined as to this feature. 



Young specimens less than 20™™ in diameter usually cannot 

 be referred with any certainty to either genus, for their papu- 

 laria, pedicellarige, and characteristic marginal spines may be 

 lacking or rudimentary. 



Cheiraster mirabilis Perrier. 



Arch<ister mirahilis (pars) Perrier, Bull. Mus. Comp. Zool., vol. ix, p. 27, 

 1881; Nouv. Arch, du Mus., vol. vi, p. 256, pi. 9, fig. 4; not pi. viii, 

 figs. 7, 8, (nor pi. x, fig. 3), 1884. 



Cheiraster coronatus (pars) Perrier, Exp. Sci. Travail, et Talisman, Echinod., 

 p. 271, 1894. 



Archaster coronatus (pars) Perrier, op. cit., 262, 1884; op. cit., p. 271, 



1894 (full deser. two varieties.) 

 Cheiraster coronatus (pars) Ludwig, Notomyota, op. cit., pp. 455, 456, 1910. 



Plate xiv ; figures 5, 5a. Details. 



The type of this species, as described by Perrier in 1881 and 

 copied in 1884, is the very same specimen (from station 148, St. 

 Kitts) as that described by him in 1894 (p. 271), as Cheiraster 

 coronatus^ ^ ''A. Premier type, bras ellonges," and there made 

 the typical form of the latter. This is, of course, contrary to 

 the ordinary rules of nomenclature, for mirahilis has three years 



