254 Prof. P. M. Duncan on the Saleniclas. 



subanal crosses the raised margin, as does that between the 

 subanal and posterior right generative plate. The margin 

 thus incised is composed of processes from the subanal and 

 the generative plates just mentioned, and is ragged from the 

 presence on it of the peculiar broad processes already noticed. 

 The anal membrane covers in the anus, except at a small spot 

 rather to the right of and behind the centre ; and there are at 

 least two imperfect concentric rows of embryonic spines and 

 ornamental processes on the membrane, the opening being in 

 the midst ; pedicellaria?, exist there also (tig. 2). 



With regard to the species described by A. Agassiz, that 

 author may be thus quoted from the ' Illustrated Catalogue of 

 the Museum of Comparative Zoology at Harvard College — 

 No. VII. Revision oi Echini^ pts. i. and ii. p. 262 : — "The 

 abactinal system covers nearly the whole of the abactinal part 

 of the test ; the anal system is eccentric. There is a marked 

 difference in the size of the genital plates, the three posterior 

 ones being much larger than the two anterior ones ; tlie reverse 

 is the case with the ocular plates. In the largest genital 

 plate there is a trace of the madreporic body, corresponding to 

 the position of the axis assigned to it by Forbes, Miiller, and 

 Wright, which cuts the symmetrical axis of the subanal plate 

 at an angle. This is the case also with the angle made by 

 the axis of the madreporic body and the first anal plate of 

 young Echini) the position of the axis passing through the 

 anal plate has no definite relation to the madreporic body. 

 The anal opening is covered by sniall plates, as in other 

 Echini. 



" The whole abactinal system is studded with embryonic 

 spines, which are longest along the exterior edge of the abac- 

 tinal system, thus separating it most distinctly from the test. 

 The sutures between the plates are sharj^ly cut with deep pits 

 at the angles of junction of the genital and subanal plate and 

 of the ocular and genital plates. The three larger genital 

 ])lates have also pits in the middle of their line of junction 

 with the subanal ])late. The genital openings are large, ])laced 

 in the middle of the plates." 



A. Agassiz gives slightly magnified views of the specimen 

 from which his description was taken ; and the abactinal region 

 is shown with the suiTOundiug spines in one figure, and sepa- 

 rate and only connected with an interambulacrum and a 

 whole or a part of an ambulacrum in a second {op. cit. pi. iii. 

 figs. 8, 11). These beautiful lithographs show that the form 

 is exceptioiial amongst the genus Salenia ; for the anal opening 

 infringes on one generative plate instead of on two, and 

 four generative plates are in contact with a fixed anal plate 



