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Show 1881.] PROF. F. J. BELL O N THE ECHINOMETRIDSE. 429 STRONGYLOCENTROTUS PURPURATUS. Absolute diameter, in millim. 50 53 55 Percentage value of Height. 44 52-8 44-1 Actinostome. 34 32 30-9 Abactinal area. 18 174 18-1 Anal area. 10 8-9 9 STRONGYLOCENTROTUS TUBERCULATUS. Absolute diameter, in millim. 26 31-5 43 54 60 Percentage value of Height. 46-1 444 50 46-3 48-3 Actinostome. 34-6 333 32-5 27-7 31-6 Abactinal area. 19-2 19 20-9 16-6 15-8 Anal area. 9-6 103 10-4 7-4 6-6 Owing to the fact that the number of species in this genus is, among the Echinoidea, so large, I have added to the Tables just given others, which show certain points in the characters of the different species which are undoubtedly of specific value. I have for these points examined every species which is represented in the national collection ; and I have to express m y hope that other observers will fill in the lacunae in our knowledge of the points now to be discussed. Relations of the Ocular Plates to the Anal Area. (a) All shut out i. Bullatus. ii. lividus (and, as we may suppose,gaimardi). iii. depressus. (ft) T wo touch iv. armiyer. v. drobachiensis. vi. erythrogrammus. vii. franciscanus. viii. intermedius. ix. purpuratus. x. tuberculatus. (y) Three touch xi. gibbosus. (c) Four touch xii. alBus1. 1 This is true of full-grown specimens. In the younger all the oculars may be shut off; but it is possible that four of these have even then a different position to the fifth, or one lying to the right of the madreporic plate. |