OCULAR AND GENITAL PLATES. 



147 



lucunter 413 specimens have ocular V alone insert, only four have ocular I alone insert, showing 

 the strong dominance of this character. In the whole number (754) examined, there are but 

 two specimens, 0.3 %, with an aberrant arrangement of oculars. In one, oculars V, IV are 

 insert, and in the other V, II alone reach the periproct (tables, pp. 163, 164). 



Text-figs. 158-161. — Ocular plate arrangement in Eddnometra lucunlcr (Linn6). Hayti, West Indies. All figures 

 X4. (Compare text-figs. 111-114, p. 115.) 



1.58. Length 41 mm., through 3, I. R. T. J. Coll., 768. Oculars all exsert, an arrested variant. 



159. Length 55 mm., tlirough 3, I. R. T. J. Coll., 769. Ocular V insert, the typical character. 



160. Length 52 mm., through 3, I. R. T. J. Coll., 770. Oculars V, I insert, a progressive variant. 



161. Length 41 mm., through 3, 1. R. T. J. Coll., 771. Oculars V, I, IV insert, an extreme progressive variant. 



Echinometra van brunti is an interesting form as it is apparently the highest species of the 

 genus, judging from the ocular plates. In 76 specimens the typical character is to have oculars 

 V, I insert, which occurs in 72 %. As arrested variants only 11 % have oculars all exsert, 

 which is the character of E. mathaei; in 12 % V only is insert, which is the character of E. 

 lucunter; and in 4 % ocular I only is insert. As a progressive variant, 1 % have V, I, IV insert. 

 It would be most interesting to get a large series of this species for comparative study, but it is 

 felt that the number seen is enough to give a fair basis for comparison. 



In Heterocentrotus mammillatus (35 specimens) 80 % have oculars all exsert, 11 % ^^re pro- 

 gressive variants with ocular V insert; in one specimen ocular I, and in one oculars V, I are 

 insert. One specimen is aberrant with oculars V, II insert. In the nearly allied Heterocentrotus 

 trigonarius (47 specimens) typically, 60 %, all oculars are exsert; in 28 % ocular V is insert, in 

 4 % ocular I and in 9 % oculars V, I are insert. In Colobocentrotus atratus (82 specimens) 99 % 

 have all oculars exsert, and in 1 % ocular V is insert, as a progressive variant. 



The Echinometridae as a family is characterized by very close adherence to the rules of 

 ocular arrangement. In the whole 1,222 specimens examined, only four aberrants were found; 

 of these, three have oculars V, II and one has V, IV insert (tables, pp. 163, 164). 



Having considered the character of ocular plates in their relation to the genitals and to 



