OCR Text |
Show 420 PROF. F. J. BELL ON THE ECHINOMETRIDiE. [Ml HETEROCENTROTUS MAMMILLATUS. Greatest diam., in millim. 44 45 59 65 75 Morphol. axis, in millim. 37 36 53 58 66 Percentage value1 of Height. 56-7 555 58-4 637 59 9 Actinostome. Long axis. 5(3 -7 63-8 50 49-1 599 Morph. axis. 55-4 611 49 53-4 566 Abactinal area. 24-3 27-7 18-8 19 227 Anal area. 10 8 IM 8-4 95 99 HETEROCENTROTUS TRIGONARIUS. Longest diam. 45 60 73 93 113 Morphol. axis. 36 50 W 78 91 Percentage value of Height. 58-3 60 56 56-4 54-9 Actinostome. Long axis. 611 55 50-7 51-9 Morph. axis. 59-7 55 51-5 50-6 Abactinal area. 20-8 20 189 211 197 Anal area. 9-7 10 9 10 8-7 As compared with H. mammillatus, we may note the striking equality of the lengths of the true and of the apparent long axes of the actinostome in this species. COLOBOCENTROTUS. The proportional measurements of the two species of this genus exhibit the greatest variability ; and here, as in the case of Heterocentrotus, there is no marked diminution in the proportional value of the diameters of the actinal and abactinal series as the test increases in size. This striking deviation from the ordinary rule does not show itself when the genus Echinometra proper comes to be studied ; and it is impossible to resist the suspicion that the " obliquity " of the long axes of Heterocentrotus and ColoBocentrotus on the one hand, and Echinometra on the other, is not altogether to be referred to the same cause. 1 The percentage values are, of course, calculated from the morphological axis. |