209 



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

 died as roiJords I heir development, viz. esrulentus niid (tcnliis. The hirvse 

 of Ihese two species are so closely alike that they are hardly distinguishable. 

 In the first stage they have elongated, clubshai)ed 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 |)laced e])auk'ts which may 

 form an almost closed ring round the posterior end of the jjodv. There is 

 no posterior transverse rod or posterolateral processes. 



The larva of the nearly related Sterechinus Neunuiiicri (which (".lark 

 regards only as a synonym of Echinus nmryarilaccus or Sterechinus 

 Agassizi, as I lliiiik Us correct name should be) is known in its second 

 stage. It agrees with the two EchinusAarvec 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 other genera! Here the matter lies quite difler- 

 ently. Within the genus Lylechinus we now know the larvae of the species 

 variegatus, anamesus and piclus in both the fust and second stages, and 

 of the species panamensis and oerrucuhitus in the first stage. The young 

 larvae have a short, rounded body, the body rod being short, branching 

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

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

 in the verruculatus-larwa. In the second stage there is a transverse rod, and 

 posterolateral lobes, while I lie presence of epaulets is not definitely set I led. 

 — The larva of Tripneusles esculentus agrees with the Lytechinus-\'dv\'?e, dif- 

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

 structure. The Tripneusles gratilla-\av\a in its first stage has the same 

 structure, while the second stage is unknown. Of Toxopneusles we know 

 with certainty only the young stage of the larvae of T. pileolus and roseus: 

 they agree completely wiih the Tripneusles-larwa in the skeletal structure. 

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

 plicate body skeleton than that of the Tripneusles-hwva, though essentially 

 of the basket-type, recalling that of the EchinomelraAarxa. and in the 

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

 lateral processes. 



It must be conceded, at least, that the facts from the larvic do not lend 

 support to Clark's view legardiug the relationship of these genera. 



(".lark's family Slrougylocentrotidae encloses the genera luhinoslrephus, 

 Pseudobolelia. Pararenlrolus. Loxcchinus. C.n'noccnirolus. Pdchgcenlrolus, 

 lleliocidaris and SIrungi/locenlrolus. Of these the genera Echinoslrephus, 

 Cxnocenlrolus, Pachgcenlrolus and Heliocidaris according to me belong to 

 the family h'Ah'mometridse, Pseudobolelia to the Toxopneustida", Paracen- 



