g6 ECHINOIDEA. II. 



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

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

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

 which seems impossible. It undoubtedly belongs to the first of these. — It might perhaps 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 pedicellarice 

 may perhaps have reference thereto; only some fragments are preserved in the British Museum, 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»-Uxpedition (de Meijere. Op. cit. p. 196) will cer- 

 tainly not be A. bellidifera either. (No specimens from St. 323 of the -Challenger* are found in the 

 British Museum.) ' 



That Aeropsis and Acestc are closely related can scarcely be doubted. The globiferous pedieellarioe 

 of Aceste (such will probably also turn out to exist in Acropsis) undoubtedly point towards Hemiaster, 

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

 petalous fasciole alone, the ethmophract apical system (in Acestc it is, however, ethmolytic, though the 

 madreporic pores do not pass beyond the posterior ocular plates (Loven. Log cit.)), the structure of the 

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

 of the mouth and of the paired ambulacra show them to be of a more primitive type than Hemiaster. 



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

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

 know the development . ( Chall.«-Ech. p. 195). We know the postembryonal development of Ecliino- 

 cardium flavescens (O. F. Mull.), EcJiinocardhnn cor datum (Penn.)*, Abatus cordatus (Verr.) (Loven. On 

 Pourtalesia), Spatangus purpureas O. F. Mull.*, Brissopsis tyrifcra (Forb.) (Agassiz. Revision of Ech. 

 PI. XIX), Hemiaster expergitus Loven* and Schizaster fragilis (Dub. Kor.)*. (On those marked with 

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

 purpureas 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 Aeropsis and Acestc show these genera to be a rather specialized branch from an 

 otherwise primitive type; this especially holds good for Acestc, 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 Aeropsis and Aceste to the Schizasterids repeatedly pointed out by Professor 

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

 other hand I am unable to see the real affinity of these genera to the iBrissina , likewise repeatedly 



1 In the Preliminary Report on the Echini collected, in 1902, among the Hawaiian Islands by U. S. Fish. Comm. 

 Steamer 'Albatross (Bull. Mus. Com]), Zool. L,. Nr. 8. 1907) published after the above was written, Agassiz and Clark de- 

 scribe two new species of Aceste (p. 258-59). This fact highly strengthens the doubt of the identity of the Challenger - and 

 ^Siboga -specimens of Aceste from the 1'acific with the A. bellidifera from the Atlantic. 



