203 



larva is characteristic of another group. Rut all Ihis can, of course, be 

 nothing more than mere suggestions— working hypotheses in the light of 

 wliicii future investigations siiould be carried out. U 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")^) states that "a satisfactory classification of the 

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

 ledge simply impossible." 1 agree with Clark herein as far as the Amphi- 

 sleinulu are concerned, while I think the classification of the Meridosler- 

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

 and Spatangida', 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 Pahvopneustida^, as 

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

 presents a progress. — 1 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 Aslrrnala, or at least the Cassidulids, do not really belong to 

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

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

 study of the development of forms like Echinolampas and Echinoneas will 

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

 relationship of these interesting forms. 



.Vnother very distinct larval type is that of the Clypeaslroids. flie 

 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. 11 nnist be claimed, of course, that if the larva* really are 

 of such classificalory value, the larva* 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 |)iest'iil work, larva* belong- 

 ing to 10 different genera, viz. Echiiwcyamus. Clypcasler. ErhiniiKtchi^iiis. 

 Dendraster, Encope, Mellila, Astridypeus, Arachnoidcs, Liujamun and Peio- 

 nella, we can form a fair judgment of the character of the Clyi)eastroid- 

 larvae in general. The result fully bears out the expectations. These larva^ 

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

 to distinguish the larv« of different genera. The Clypeastroid-larva* 



») Mem. Mus. Comp. Zool. XLVI. 1917, p. 98. 



26* 



