209 



Of the species referred to the genus Echinus s. sir. two have been stu- 

 died as regards their development, vix. cscidentus and aciilus. The larva 1 

 of these two species are so closely alike lhal they are hardly distinguishable. 

 In the first stage they have elongated, clubshaped body rods, but no basket 

 structure; in the second stage they have four epaulets, at the base of the 

 four main arms, and besides a pair of laterally placed epaulets which may 

 form an almost closed ring round the posterior end of tin- body. There is 

 no posterior transverse rod or poslerolaleral processes. 



The larva of the nearly related Slenrhinuf, .\('iinuti/eri (which Clark 

 regards only as a synonym of Kchiinia margaritaceus - - or Slcrcchinus 

 Ayassizi, as I think its correct name should be) is known in its second 

 stage. It agrees with the two Ecftinus-larvse in all essential features. 



The larva? of these forms accordingly agree very well in their main 

 characters as should be expected, since they are indisputably closely rela- 

 ted. But now those of the oilier genera ! Here the matter lies quite differ- 

 ently. Within the genus LyU'chinus we now know the larva? of the species 

 varieyalus, anamesus and piclus in bolh the first and second stages, and 

 of the species panamensis and m'rnicuhitus in the first stage. The young 

 larva? have a short, rounded body, the body rod being short, branching 

 at the end; the recurrent rod is well developed but does not unite with 

 the branch from the body rod so as to form the basket structure, except 

 in the verruculalus-larva. In the second stage there is a transverse rod, and 

 posterolateral lobes, while the presence of epaulets is not definitely settled. 



- The larva of Tripneustes esculentus agrees with the Li/l<rhinus-]ar\x, dif- 

 fering only in the body skeleton of the first stage forming a typical basket 

 structure. The Tripneusles gratilla-larva in its first stage has the same 

 structure, while the second stage is unknown. Of . To.ro/j/in/.sVrs- we know 

 with certainty only the young stage of the larvae of T. pilcolus and roscus: 

 they agree completely with the Tripneustes-lSLtva in the skeletal structure. 

 Finally the larva of Evechinus rhlomlicus has in its first stage a more com- 

 plicate body skeleton than lhal of the Tripneustes-larvSL, though essentially 

 of the basket-type, recalling that of the Echinomelra-l&TVSL, and in the 

 second stage (almost certainly) a posterior transverse rod and poslero- 

 laleral processes. 



II must be conceded, at least, lhal the facts from the larva 1 do not lend 

 support lo Clark's view regarding I he relationship of these genera. 



Clark's family Strongylocentrotidse encloses the genera Echinostrephus, 

 Pseudobolelia, Ptintcrnlrolus. Lo.icchinus, (lu>nuccnlnttm, Pachycentrotus, 

 Heliocidaris and Strongylocentrotus. Of Ihese the genera Echinostrephus, 

 C&nocentrolus, Pachycentrotus and Ilcliocidarix according to me belong to 

 the family Echinometridae, Pseudoboletia lo the Toxopneustidae, Pmmr/i- 



27 



