54 



ECHINOIDEA. I. 



coalesced, so that a series of large holes is found along the median line — and tliey mav also be 

 fonnd of the form, fignred of A. coriacrmu). The pedicellariæ (the tridentate ones) with short neck; 

 the stalk of the coramon strnctnre. The tube feet in three series. The spicnles (PL XI. Fig. 15) are 

 not so compact fenestrated piates as in A. ftnestralum ^ the holes are mnch larger and fewer. In the 

 lower part of the tnbe foot the spicnles are more narrow, at last only fine, thorny, irregular needles, 

 often a little widened as small fenestrated piates in one end or in both ends, or they have a larger hole 

 in the middle. Below they seem to be arranged in fonr longitndinal series, above they inclose the 

 whole foot as a close mail. The sncking disk well developed in the actinal tnbe feet. The primary 

 spines on the actinal side form a ver)^ consjDicuons, regnlar series along the onter edge of the interambn- 

 lacral areas; in the ambnlacral areas only 5 — 6 large spines are fonnd scattered on the onter piates. 

 They are cnrved, and end in a little hoof. Resembling more nearh- tlie primary spines oi Plioriiwsoiua 

 than the characteristic flaring trnmpet-shaped spines of Astlicnosoma ^ Agassiz says of these spines 

 (Chall. Ech. p. 88). As his ■ P/ioniiflso/iia:> contains so widely different forms as P/i. flaccnta and Iiopla- 

 cantha this statement gives no clear information; the meaning of it is that they are similar to those 

 of A. fenestrahim\ the hoof is little, short, and broad. 



Agassiz says of this species that it is vallied to AstJicnosoina gnibii in having an extremely 

 thick leathery cnticle* (1. c); according to the informations given here there is no nearer relation 



between these two species. Agassiz fnrther thinks that it is < qnite possible that this may be the 



adnlt of ^Istliruosoma tcssclafuin (1. c). After having examined the type specimen of this species I 

 can sav with certaint}- that this is not the case; the two species are not even so very nearly related 

 even if they possibly belong to the same genns. — Tetradactylons pedicellariæ have not been found 

 in this species. The tridentate pedicellariæ occur in two forms, between which there seem to be no 

 transitions. The large form is qnite similar to the large tridentate pedicellariæ in A. fcncsfratmii 

 (PI. XIII. Fig. 5); the smaller form (PI. XIII. Fig. 6, PI. XH'. Fig. 15) is very pecnliar, the blade deep, 

 filled by a ricli net of meshes, and with a highly irregular edge without snch large sinuations as are 

 found in A. fcnestratuvi and conacniu/; the widenings from the upper end of the apophysis continue 

 directly into the edge of the blade. When the pedicellaria is shnt, the edges join completely, there is 

 only at the basal part a small open space. This form is a little more long-necked than nsual. The 

 triphyllous pedicellariæ are quite similar to those of A. fcncstraluiii and coriacciii/r, the stalk of the 

 pedicellariæ of the common strnctnre. Spicnles and sncking disk as in A. fcncstrahivi; the tube feet 

 in three series. All the primary spines on the actinal side are broken in the only .specimen known, 

 so that it is impossible to sav anything of the form of the point; snrely, however, they are not skin- 

 covered. — For the present it is impossible to decide whether this species is to be classed with A. 

 fcncstratum and coriaccum-^ but several things speak in favour of this supposition, and it will therefore 

 be most correct provisionally to refer this species to the genus Aræosoma. That the membranous 

 interspaces between the piates are especially large in this species speaks, of course, only in favour of 

 the supposition that it really belongs to this genus. 



Among the specimens kept in British Museum under the name of Astlienosoiiia hyslrix^ a piece 

 was found (from Barbados, 137 fathoms), which is no doubt a new species, and probably also belongs 

 to this genus. It is verj- similar to Calvcria hysfrix, but is of a darker colour (brownish violet). 



