io 8 ECHINOIDEA. II. 



Figs, i — 4) as Periastcr limicola*. I quite agree with the eminent author herein, and having examined 

 the specimens in the British Museum I am able to add some more differences to those now found by 

 Professor Agassiz between the « Challenger » specimens and the true P. limicola. The labrum ends 

 off the first adjoining ambulacral plates. There are four large subanal tube-feet. One specimen has 

 two genital pores, the other has four, the two anterior being quite small. The latero-anal fasciole has 

 quite disappeared in one specimen, in the other there are distinct traces of it. The frontal tube-feet have 

 a well developed disk, strongly lobate in the edge, the rosette-plates reaching only the beginning of the 

 lobes. The spicules are very numerous, rather much branched, otherwise like those of limicola. The 

 globiferous pedicellarise are of the Schizasterid type, with a very large space within the blade (PI. XIV. 

 Figs. 1,4); there is one tooth on either side of the terminal opening. The stalk has a limb above, where 

 the muscles from the head are fastened, and a small ring below. The tridentate pedicellarise (PI. XIV. 

 Fig. 21) are rather similar to those of P. limicola, viz. the slender form. The long and slender valves 

 join only at the point; the edge is in the lower part very coarsely and irregularly serrate; there is 

 a little meshwork, sometimes rather coarse, in the blade. Rostrate pedicellarise have not been found; 

 the ophicephalous pedicellarise (PI. XIV. Figs. 5, 36) are of the usual Spatangoid type, and there is a 

 prolongation from the lowermost of the arcs. The stalk is not distinctly cupshaped above. The tri- 

 phyllous pedicellarise do not present peculiar features. 



The differences pointed out by Professor Agassiz and here, together with the geographical 

 distribution: one a deep-sea form from the Gulf of Mexico, the other a littoral form from the Arafura 

 Sea, leave 110 doubt that this is another species; if it be a new species is not so certain. It is very 

 like the Schizastcr Jukcsii Gray both in the characters of the test and of the pedicellarise, and even 

 the locality is the same; indeed, I think it almost beyond doubt that it is really identical with that 

 species. — (In Revision of Echini » Schizastcr Jukcsii is made a synonym of Sch. vcntricosus (lacn- 

 nosits L.); this is, however, certainly not correct; the verification thereof will be given in Part II of 

 the Siam-Echiuoidea). Whether Schizastcr Jukcsii ought really be reckoned to the genus Periastcr, as 

 is done, in fact, by Agassiz in the (.Challenger -Echinoidea, is not easy to determine, these genera 

 being upon the whole very closely related. Perhaps the globiferous pedicellarise may indicate the 

 correctness of referring Sch. Jukcsii to Periastcr ; in any case they differ considerably from those of 

 Schizastcr lacuuosiis a. o. (comp. below). But upon the whole I do not venture to enter in a more 

 detailed manner on a discussion of the rather difficult question of the genus Periastcr, my knowledge 

 of the fossil forms being too insufficient. 



27. Brisaster (Schizaster) fragilis (Dub. Kor.). 



PI. I. -Figs. 6—7. PI. XIII. PI. XIV. Pigs. 3, 7, 11, 13—16, iS, 20, 24—25, 31, 37, 39, 43, 46, 50—51. 

 Synonyms: Brissus Jragilis Dub. Kor. 



Tripylus Jragilis Sars. 



Principal literature: Diiben & Koren: Skandinaviens Echinodermer. 1844. p. 280. Tab. X. 47 — 



49. — Gray: Catalogue Rec. Echinida. 1855. p. 61. -- Liitken: Bidrag til Kundskab ora Echiniderne. 



p. 175 (107). -- Sars: Norges Echinodermer. p. 96. — Agassiz: Rev. of Echini, p. 157, 363. PI. XXI. 3, 



XXVI. 42. — Challenger -Echiuoidea. p. 201, « Blake -Ech. p. 74. PI. XXVIII. 8— 14. — Loven: Etudes 



