Genera of Recent Clypeastroids. 599 



species in Arachnoides, it is obviously the type. There is 

 room for difference of opinion as to whether Arachnoides 

 should date from Leske or Agassiz ; but as 1 have no doubt 

 that the " Geuus 1 " of the former is Arachnoides, Klein, and 

 as Leske himself uses that name on p. 8, it seems to me right 

 to date the genus from the ' Additaraenta.' Fourtau (lOO^) 

 has attempted to substitu.te Echinodiscus for Arachyioides, 

 but as his argument is based on the acceptance of pre- 

 Linnean names, it does not concern us here. Ortmann 

 (1902) believes that Echinarachnins is not distinguishable 

 from Scutella; but I cannot agree Avith him, for the differences 

 between the petals of a typical Scutella (like subrotunda) and 

 those of Echinarachnins are sufficiently important from the 

 phylogenetic point of view to warrant generic separation, in 

 spite of the existence of perplexing connecting forms. The 

 genus Dendraster was proposed by Agassiz and Desor (18J;7) 

 for the remarkable sand-dollar of the North Pacific called 

 Scutella excentrica by Eschscholtz. In the ' Revision •" this 

 genus is considered a synonym of Echinarachnius ; but I 

 cannot believe this is desirable, for excentrica is quite unique 

 in several important characters, and in my judgment 

 Dendraster should be retained. 



The genera Peronella, Gray, Aaomolanthus, Bell, Alex- 

 andria, Pfeffer, and Astriclypeus, Verrill, were all monotypic 

 when established, so there is no room for doubt as to their 

 types. I am quite unable to follow Bell's (1883, Ann. & 

 Mag. Nat. Hist., February) line of argument, by which he 

 endeavours to dissociate Peronella from Gray. To my mind 

 it is perfectly clear that Gray established Peronella as a 

 subgenus for Laganum ])eronii, Agass. I am by no means 

 clear as to the exact limits of Peronella as a generic term at 

 the present day, but I am inclined to think it may well be 

 used to include the species, otherwise referred to Laganum, 

 which have only four genital pores. 



In spite of their long-continued use, the genera Eacope 

 and Mellita, so far as I can discover, have never had any 

 types designated. For the former I would choose the species 

 called Echinodiscus emarginatus, Leske, Avhicli seems to have 

 been the longest known of any species. For Mellita I select 

 quinqniesperforatus , Leske, both because it has page prece- 

 dence over sexiesperjoratus and because it seems to be a 

 commoner and more generally known species. I greatly 

 regret that the shorter and much more euphonious names 

 given by Gmelin ten years later to these two species may not 

 be used, but it would involve a deliberate violation of the 

 Code. The fact that Leske wrote the specific name in two 



