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Show 1880.] MR. F. J. BELL ON A NEW GENUS OF ECHINOIDS. 47 between these there are a few pores not very 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 posterolateral, 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 ' l, and which, as is well known, is so distinctly marked in Palceechinus among older forms2. Interambulacral system.-The interambulacral areae are composed of large broad plates and are considerably wider than the ambulacral, 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 apical 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 Echinolampas or in Conoclypeus sigsbei (cf. fig. 2, p. 190, t. oi): 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 below 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. W e have already had some examples of the archaic characters presented by E. depressa ; and when we compare it on this point with E. oviformis, 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. Comino* 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 Echinolampas or Rhyn-chopygus, though it seems to be greater than in Conoclypeus sigsbei. i Loven, " Etudes sur les Echinoidees," Kongl. Svens. Vetensk. Handlingar, 2 Dublin Quarterly Journal of Science, v. (1805), plate vii. fig. B. |