1880.] MR. F. J. BELL ON A NEW GENUS OF ECHINOIDS. 47 



between these there are a few pores not rery regularly or definitely 

 arranged, but apparently not so extensive as in C. siysbei. 



The ocular plates are very distinct ; but two of the pores, the 

 anterior median (which is almost obliterated), and the left postero- 

 lateral, are smaller than the rest ; those of the right side are both 

 interesting as exhibiting indications of their primitively double 

 character — a point to which Prof. Loven has called attention in his 

 invaluable ' Etudes ' ', and which, as is well known, is so distinctly 

 marked in Palaechimis among older forms ^. 



Interambulacral system.— ')L\ie interambulacral arese are composed 

 of large broad plates and are considerably wider than the ambulacra), 

 but there are no points of especial importance to be noted with 

 regard to them ; the odd posterior genital plate has disappeared, 

 and the madreporic plate occupies the whole of the central portion 

 of the ai)ical area. The two postero-lateral pores are a very 

 little more widely separated from one another than are the more 

 anterior pair ; but the divergence is not in any way so marked as 

 it is either in Echimlampas or in Conoclypeus sigsbei {cf. fio-. 2, 

 p. 190, t. c): this may be taken as an expression of the greater 

 equality of the several genital ocular plates, and as, pro tanto, an 

 indication of a more archaic arrangement. 



The anus is elongated from side to side, is of some size, and is 

 placed just belo\y the margin of the test : in C. leskii the anus is 

 rounded; in C. sigsbei it would appear to be elongated transversely; 

 but in the greater number of the members of the genus Conoclypeus 



it would appear, from the definition of Agassiz and Desor " anus 



infra-marginal, allonge' dans le sens du diametre antero-posterieur " 

 —to be elongated along the axis at right angles to that in which it 

 is elongated in our specimen. 



The whole test is covered regularly by primary tubercles, all equal 

 in and of some size ; the only region in which there is the very 

 slightest irregularity is in the intraambulacral region just in front 

 of the mouth, where the tubercles are a little less closely packed ; 

 this arrangement is exceedingly interesting when compared with 

 what obtains in Echinolampas. We have already had some examples 

 of the archaic characters presented by E. depressa ; and when we 

 compare it on this point with E. ovifonnis, we find that in the 

 former the tubercles are evenly distributed over the whole test, and 

 that there are no bare bands, while in the latter a tract free 'from 

 tubercles extends both forwards and backwards from the region of 

 the actinostome. 



Coming now to the final consideration, we have to inquire into 

 the position of the apical system and of the actinostome. They have 

 both left their central position, but have proceeded a very slight 

 distance forwards ; and the distance from the centre of the test' is 

 by no means so great as it is in the genera Echitwlampas or Rhy7i- 

 chopygus, though it seems to be greater than in Conoclypeus sigsbei. 



• Loveil, " Etudes sur les Echinoidees,"' Kongl. Svens. Yetensk. Handlinear 

 Bd. ii. no. 7, p. 67. ' 



^ Dublin Quarterly Journal of Science, v. (L-^Cm), plate vii. %. B. 



