96 ECHINOIDEA. II. 



slender form of tridentate pedicellariæ; but I have not seen tliein without neck, and also the shape is 

 ratlier different from that seen in the specimens examined by me. The Fig. 46. PI. XLIV is said in 

 the explanation of piates to be a valve of both the forms figured in Fig. 27. PI. 42 and Fig. 25. PI. 43, 

 which seems irapossible. It nndoubtedly belongs to the first of these. — It might pcrhaps be doubted 

 whether the specimen(s?) from <:Chall.?-St. 272, in the Pacific (between Hawaii and Paumotu), 2600 

 fathoms, are really identical with the Atlantic specimens. The above mentioned figures of pedicellariæ 

 niay perhaps have reference thereto; only some fragments are preserved in the British Mnsenm, so 

 that the question cannot be solved from that material alone. In case the Pacific specimens prove to 

 be another species, the .specimen from the Siboga -Fixpedition (de Meijere. Op. cit. p. 196) will cer- 

 tainh' not be A. bellidifcra either. (No specimens from St. 323 of the - Challenger» are fonnd in the 

 British Museum.)' 



'T:\\3X Aeropsis 2>.Viå. Aceste QX& closely related can scarcely be doubted. The globiferous pedicellariæ 

 oiAcestc (such will probabh- also turn out to exist in Acropsis) nndoubtedly point towards Honiastcr, 

 with which genus Aerofsis and Accstc agree in several important characters: the existence of a peri- 

 petalous fasciole alone, the ethmophract apical system {\\\ Accste it is, however, ethmolytic, though the 

 madreporic pores do not pass bevond the posterior ocular piates (L,ovén. Ivoc. cit.)), the structure of the 

 spines, and the prominent suckers of the odd ambulacrum. On the other hånd the primitive condition 

 of the month and of the paired ambulacra show them to be of a more primitive type than Heniiaslcr. 



The enormous development of the frontal tube-feet, is, according to Professor Agassiz, an 

 eminently embryonic feature, it exists in the \oungest stages of all the Spatangoids of which we 

 know the development . (Chall. -Ech. p. 195). We kuow the postembryonal development of Ec/iiiio- 

 cardinm flavescens (O. F. Miill.), Echinocardhim cordatum (Penn.)*, Abatus cordatus (Verr.) (Loven. On 

 Pourtalesia), Spatangus purpurais O. F. Miill.*, Brissopsis lyrifcra (Forb.) (Agassiz. Revision of lich. 

 PL XIX), Hemiaster expergitus Loven* and Schizaster fragilis (Diib. Kor.)*. (On those niarked with 

 an * information will be found in this work.) But in Eclniiocardiwm flavescens, cordatum, Spatangus 

 purpur eus and Abatus cordatus at least these suckers can by no means be said to be very large and 

 prominent in the young specimens. On the contrary, it seems to be the rule that those forms which 

 have, when fullgrown, large suckers get them early developed, whereas those which have only small or 

 little prominent suckers when grown up have them small also in the young stages — as might, indeed, 

 be expected. It seems then more safe to conclude that the small suckers represent the more primitive 

 condition, the less specialized stage being, of course, prior to the more specialized. Thus, I think, the 

 large suckers of Aéropsis and Aceste .show these genera to be a rather specialized branch from an 

 otherwise primitive type; this especially holds good for Aceste, whose test has got its very peculiar 

 form evidently on account of the extreme development of the odd ambulacrum and its tube-feet. 



The affinities of Aéropsis and Aceste to the Schizasterids repeatedly pointed out by Professor 

 Agassiz seem very probable; also the globiferous pedicellariæ are in accordance with this. On the 

 other hånd I am nnable to see the real affinit>- of these genera to the iBrissina , likewise repeatedly 



' In the Prelimiiiary Report 011 tlie Rchiui coUected, in 1902, among the Hawaiian Islands by U. S. Fish. Comni. 

 •Sleanier 'Albatross:- (Bull. Mus. Comp, Zool. L. Nr. 8. 1907I published after the above was written, Agassiz and Clark de- 

 scribe tvvo new species of Aces/e (p. 25S-59). This faet highly strengthens the doubt of the identity of the - Challenger - und 

 »Siboga --specimens of Aceste from the Pacific with the A. he/lidifeia from the .\tlantic. 



