ECHINONEUS. 101 



of a well-developed lantern in very young individuals of Echinoneus reported 

 by Mr. Agassiz in 1909 (Amer. Journ. Sci. ser. 4, 28, p. 490) indicates a nearer 

 relation to the Regular Echini than was suspected. The Recent members of 

 the family have been so lately monographed by Westergren (1911. Mem. 

 M. C. Z., 39, no. 2, p. 35-68, pis. 1-31) that there is no occasion to discuss 

 them further here. Only two genera are recognized and one of these is known 

 from but a single specimen. 



Key to the Genera of Echinoneidae. 1 



Poriferous areas depressed; all pore-pairs in peripodia Echinoneus. 



Poriferous areas flush with the surface of the test; pore-pairs of mid-zone without 

 peripodia Micropetalon. 



Echinoneus. 



Leske, 1778. Add. ad Klein, p. 7, 109. 

 Type, Echinoneus cyclostomus Leske, 1778. Op. cit., p. 109. 



The idea of dating Echinoneus from Van Phelsum, 1774, seems to me 

 untenable, as pointed out in an earlier publication (1911. Ann. Mag. Nat. Hist., 

 ser. 8, 7, p. 596). Leske included two species in the genus but as the second 

 is undoubtedly a synonym of the first, the latter is of course the type. In his 

 discussion of the genus, Westergren (op. cit.) recognizes only a single species 

 but he makes a casual reference (p. 44) to E. abnormalis, without committing 

 himself as to the validity of that form. After the examination of seven speci- 

 mens, I am still uncertain as to the status of E. abnormalis, but am inclined 

 to consider it a valid species. In any case, Echinoneus is the only known 

 genus of Echini in which so fundamental a character as the perforation of the 

 tubercles is variable. The significance of such variability is not clear but it 

 may indicate that the genus arose at about the time when the groups of 

 Regular Echini with imperforate tubercles were being differentiated and before 

 the character was fixed. The pedicellariae too indicate that Echinoneus is 

 not a highly specialized type. All four kinds of pedicellariae are present; the 

 globiferous are of a very primitive form not widely different from the tri- 

 dentate and the same is true of the ophicephalous. Westergren has figured the 

 pedicellariae, as well as all other morphological details, so elaborately and so 

 accurately, that it would be quite superfluous to discuss them here. 



1 In this and all subsequent keys only Recent forms are considered. 



