96 



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. XLI\' 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 pedicellariae 

 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^-Expedition (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.) ' 



'Y:\\sX Aeropsis 2.\\(^ Accstc d^xQ closely related can .scarcely be doubted. The globiferous pedicellarise 

 oiAccste (such will probably also turn out to exist in Ar'ropsis) undoul)tedly point towards Hr»iiastcr, 

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

 petalous fasciole alone, the ethmophract apical system (m Acrste it is, however, ethmolytic, though the 

 madreporic pores do not pass Ijeyond the posterior ocular plates (Loven. L,oc. 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 Hcmiosicr. 



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

 eminentl}- 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 po.stembryonal development of Ecliiiio- 

 cardium flavesceiis (O. F. Miill.), Echinocardiiim cordatum (Penn.)*, Abatus cordatits (Verr.) (Loven. On 

 Pourtalesia), Spatangus purpurczis O. F. Miill.*, Brissopsts lyrifcra (Forb.) (Agassiz. Revision of Ech. 

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

 an * information will be found in tliis work.) But in Ecliiiiocardium flavescens, cordatum, Spatangus 

 purpurcus 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 tlie more primitive 

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

 large suckers of Aeropsis and Acestc show these genera to be a rather specialized braucli 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 Acestc to the Schizasterids repeatedly pointed out by Professor 

 Agassiz seem very probable; also tlie globiferous pediccllaria; are in accordance witli lliis. On llie 

 other hand I am unable to see the real affinit> of these genera to the <iBrissina^^^ likewise repeatedly 



' In the Preliminary Report on the F.diini collectetl, in 1902, among the Hawaiian Islands by U. S. I'ish. Conini. 

 Steamer .Albatross (Hull. Mus. Coniij, Zool. \,. Nr. 8. 19071 pubUshed after the above was written, Agassiz and Clark de- 

 scribe two new species of Acestc (p. 258-59). This fact highly strengtlRiis tin- dmibt of tlu- id(.ntit\ (if tlu- Clialknger - and 

 • Sibogav-speciinens of Accsle from -the Pacific with the A.bellidi/era from the .\tlantic. 



