OCR Text |
Show 426 PROF. F. J. BELL ON THE ECHINOMETRIDsE. [M STRONGYLOCENTROTUS ARMIGER. Absolute diameter, in millim. , 20 32 47 69 76 Percentage value of Height. 48 46.8 468 405 46 Actinostome. 34-6 328 319 28-9 30-2 Abactinal system. 19-2 18-7 191 15-9 161 Anal area. 10*5 109 89 7-2 7-2 STRONGYLOCENTROTUS BULLATUS. Absolute diameter, in millim. 38 94 115 Percentage value of Height. 50 45-2 Actinostome. 31-6 30-8 2304 Abactinal area. 23-7 18 18-2 Anal area. 121 10-6 9-5 STRONGYLOCENTROTUS DEPRESSUS. A dry test, denuded of spines, is very probably to be referred to this species ; I proceed, however, to point out a number of characters by which it appears to differ from the descriptions of S. depressus as given by Prof. Alex. Agassiz, or the E. disjunctus of Prof. Fig. 1. Ambulacral area of 8. depressus, to show the disposition of the pairs of pores. von Martens. The test is not so depressed; the primary tubercles are not so numerous ; the poriferous zone is not specially broad ; and it is not the uppermost, but the lowermost pair of pores that is "dis-junctum." As to this last point, however, there is possibly some error of observation, as it is difficult to see the exact position of the pair of pores in question, since they lie altogether at the edge of the plate. If the difference is real, it is probably one of specific importance. Prof. Agassiz remarks that in specimens with a depressed test, "the inner and one outer pairs of pores " are disconnected. |