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trotus and Loxechinus to the Echinidse; the relation of Strongylocentrotus 

 appeared uncertain, though I have thought it probably nearest related to 

 the Toxopneustidse. Unfortunately, the larvae of most of these genera are 

 still unknown; but we know those of Paracentrotus lividus, Heliocidaris 

 tuberculata ( — the reduced larva of H. erythrogramma does not count in 

 this connection — ) and some '' Strongylocentrotus" -species. 



The larva of Paracentrotus lividus agrees with the Echinus-type; the body 

 rod is elongated, clubshaped, and no basket structure is found in the first 

 stage; there is no posterior transverse rod or posterolateral processes in 

 the second stage. Anterior but no posterior epaulets (as in Psammechinus 

 miliaris). In the larva of Heliocidaris tuberculata the body skeleton in the 

 first stage forms a very complicate basket structure, as in the Echinometra- 

 larva; in the second stage there is a posterior transverse rod and postero- 

 lateral lobes; vibratile lobes are present, but no epaulets. 



Within the genus Strongylocentrotus we know the larvae of the species 

 drebachiensis and franciscanus fairly completely, that oi pulcherrimus nearly 

 so and that of purpuratus in its first stage. They all agree in the body 

 skeleton forming no basket-structure, the body rod being clubshaped, elong- 

 ate (less so in franciscanus); in the second stage there is no posterior trans- 

 verse rod or posterolateral processes, but both anterior and posterior epau- 

 lets as in the Echinus-larva (presence of epaulets in the pulcherrimus-larva 

 uncertain). 



To the genus Strongylocentrotus Clark also refers the mediterranean 

 species granularis, otherwise unanimously regarded as the type of a separate 

 genus, Sphaer echinus. According to my view this genus belongs to the 

 family Toxopneustidse, representing a polyporous development within that 

 family. The larva of this species differs most conspicuously from those of 

 the above named Strongylocentrotus-species. The body skeleton forms a 

 basket-structure in the first stage; in the second stage a posterior trans- 

 verse rod is formed, and there are posterolateral processes, vibratile lobes 

 and anterior but no posterior epaulets. That the postoral rods are fene- 

 strated is another conspicuous difference from the Strongyiocentrotus-larvae, 

 though of minor morphological importance. Thus it is evident that the 

 characters of the larva of Sph. granularis bear decided testimony against 

 classifying that form with the "Strongylocentrotida", or even referring it 

 to the genus Strongylocentrotus itself, while on the other hand there is per- 

 fect agreement between the larval characters of .V. granularis and those 

 of the other Toxopneustid-larvae thus far known. 



To the genus Strongylocentrotus Clark also refers the Japanese species 

 depressus, which, according to my view, represents the type of a separate 

 genus, Pseudocentrotus, of the family Toxopneustid*. The little bit of in- 



