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Show 1881.] PROF. F.J. BELL ON THE ECHINOMETRID^E. 419 of three or more than three primary plates e. g. Strongylocentrotus. Group II. Morphological axis set obliquely to long axis of the test.... E C H I N O M E T R I N S E, Group III. Morphological axis set at right angles to long axis of the test' HETEROCENTRINSE. On the present occasion the observations now to be recorded are based on the classification of the ' Revision ;' the further details of altered classification now proposed can only be worked out when sufficient details as to the Triplechinidse have been presented to the Society ; the Temnopleuridse have already 2 been touched : but even then Temnechinus and Trigono cidaris must have a place found for them ; perhaps that will, after all, turn out to be not among the Echinidse at all. I now proceed to the details of some of the genera of the so-called family " Echinometradse." HETEROCENTROTUS. If the student lets this paper follow in succession the third part of these " Observations," he will, on examining the subjoined percentage values, be struck by the fact that there is not by any means that marked diminution in the proportional values of the actinal and abactinal systems to which attention could scarcely fail to have been drawn in the study of the Temnopleuridse. The character of these latter, though perhaps hardly so well marked, will be seen when the species of the genus Echinometra come under inspection. 1 have not been able to detect any very striking differences in the characters of the buccal apparatus of H. mammillatus and H. trigo-narius. The most important is, probably, their difference in size ; for while a test of LL. mammillatus, with a height of 26 millim., gave as a measurement from the tip of the tooth to the top of the epiphysis the almost paradoxical amount of 29 millim., two tests of 17. trigonarius, 21 and 25 millim. high respectively, gave for the same distance 21 and 23 millim. in the two cases. In both cases there are ascending and descending processes, which are perhaps a little better developed in H. mammillatus, as is also the hammer-headed widening of the free end of the radius, and its division by a median notch. 1 It is not yet time to forget the words of J. Midler:-" Der Korper querer Lage symmetriscb, welcher von der erstgenannten Gattung (Echinometra) bereits von Brandt erkannt, und durch Corpus transversum ausge-druckt, von Agassiz aber nicht bemerkt worden, der diese Formen mit Echinometra fur schief angesehen hat" (Abb. Berl. Akad. Wiss. 1853, p. 128). 2 P. Z. S. 1880. |