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larva is characteristic of another group. But all this can, of course, be 

 nothing more than mere suggestions working hypotheses in the light of 

 which future investigations should be carried out. It must be remembered 

 that the classification of the Spatangoids is very far from being settled. 

 In fact, H. Lyman Clark in his work on the Spatangidse ("Hawaiian 

 and other Pacific Echini") 1 ) states that "a satisfactory classification of tin- 

 Echini here included in the Spatangina is in the present stale of our know- 

 ledge simply impossible." I agree with Clark herein as far as the Amphi- 

 sternata are concerned, while I think the classification of the Meridoster- 

 nata in fairly good order. The amphisternous "families" Hemiasteridae 

 and Spatangidae, as comprised in Clark's work, are certainly unnatural, 

 which is, however, not to be wondered at, his classification being "purely 

 one of convenience, worked out in the endeavour to make an artificial key 

 to all the genera and species of living Spatangoids." But no better classi- 

 fication exists, and it seems at least that the family Palaeopneustidae, as 

 comprised by Clark, is fairly natural, and thus far his classification re- 

 presents a progress. I would expect that the study of the larvae will 

 prove of great importance for establishing the natural relationship between 

 the numerous forms of Spatangoids. 



That the Asternata, or at least the Cassidulids, do nol really belong to 

 the Spatangoids, but are more nearly related to the Clypeastroids seems 

 rather probable alone from the study of the Echinobrissus-lavva. The 

 study of the development of forms like Echinolumpas and Echinoneus will 

 be of the greatest importance for settling the question of the natural 

 relationship of these interesting forms. 



Another very distinct larval type is that of the Clypeastroids. The 

 order of the Clypeastroidea being a very well limited one, and there being 

 no doubt that the forms referred to that group are really naturally related, 

 the study of the Clypeastroid-larvae will afford a critical test to the theory 

 of the value of the larvae as lending proof of the natural relations of the 

 adult forms. It must be claimed, of course, that if the larvae really are 

 of such classificatory value, the larvae of the Clypeastroids should form 

 a uniform group, as do the adult forms. As we now know, through the 

 previous researches and those recorded in the present work, larva? belong- 

 ing to 10 different genera, viz. Echinocyamus, Cly/waxlcr. Echinarachnius, 

 Dentil-aster, Encope, Mellila, Aslriclypeus, Aniclinoidc*. Ln<i<tnum and Pcro- 

 nella, we can form a fair judgment of the character of the Clypeastroid- 

 larvae in general. The result fully bears out lln- expectations. These larvae 

 form a very uniform group, so uniform that it is even in some cases hard 

 to distinguish the larvae of different genera. The Clypeastroid -larva- 



x ) Mem. Mus. Comp. Zool. XLVI. 1917, p. ( JS. 



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