PSAMMECHINUS. 243 



Echinus, into which they put a rather heterogeneous group of species. In 1855, 

 Desor raised the group to generic rank and in 1862, Dujardin and Hupe rear- 

 ranged the species, but in neither instance was there any revision of the group 

 attempted. In 1863 however both A. Agassiz and Liitken, quite independently 

 recognized the unnatural association of species in the group, and removed from 

 it the species with deep gill-slits. Agassiz, whose paper has a few months 

 priority, is clearly the "first reviser" and he definitely restricts Psammechinus 

 to the forms with shallow gill-slits (though he gives no diagnosis) and names 

 miliaris as the first species. To the species with deep gill-slits he gives the name 

 Lytechinus, and under it names three species, all of which Mortensen, and all 

 other recent writers, regard as synonyms of variegatus. While the action of 

 Agassiz does not settle the type of Psammechinus, it does forever preclude the 

 use of variegatus as the type of that genus; unless indeed the name is used in the 

 same sense and with the same contents as when originally proposed! Liitken's 

 paper, while entirely in agreement with Agassiz's, very naturally gives a different 

 name (Psilechinus) to the variegatus group, which of course is a synonym of 

 Lytechinus, but he also fails to designate a type for the restricted Psammechinus. 

 He suggests verruculatus as a typical example of the genus and it might have been 

 accepted as the type, were that not impossible since verruculatus is not among 

 the species known to Agassiz and Desor, and therefore is not in their genus. 

 In 1867, Verrill (Trans. Conn. Acad., I, p. 302) definitely designates "Echinus 

 variegatus" as the type of Lytechinus. In 1869, Pomel (Rev. des Ech., p. 42) 

 says that Psammechinus Agassiz and Desor is not a homogeneous group and 

 ought to be restricted to the type of miliaris and microtuberculatus. Schiz- 

 echinus is very unnecessarily proposed for variegatus and its allies. It seems 

 impossible to doubt that at the time of the publication of the "Revision of the 

 Echini" (1872) all students of the Echini were agreed that the name Psammechi- 

 nus belonged to miliaris and its allies, while variegatus typified a very different 

 group, for which three different names had been suggested, the earliest being 

 Lytechinus A. Ag. In the "Revision of the Echini" Mr. Agassiz thought best 

 to unite Psammechinus with Echinus, and Lytechinus with Toxopneustes and 

 these unions have been almost universally accepted. Mortensen (1903, " Ingolf " 

 Ech., pt. 1, p. 106, 114) has however shown excellent reasons, in the structure 

 of the ambulacra and in other characters for separating the groups thus united, 

 but it is clearly impossible to follow his nomenclature. While it seems possible 

 to argue as to whether any type has ever hitherto been definitely and correctly 

 assigned to Psammechinus, the type of Lytechinus is beyond doubt. Lambert's 



