OCR Text |
Show 1881.] PROF. F. J. BELL ON THE ECHINOMETRIDsE. 421 COLOBOCENTROTUS ATRATUS1. Longest diam. 42 53 67-5 Morphol. diam. 39 47 61 Percentage value of Height, 40 531 50 Actinostome. Long. 423 51 43-4 Morphol. 423 48'9 41-8 Abactinal area. 18 21-2 22'1 Anal area. 7'9 8-5 8 COLOBOCENTROTUS MERTENSI. Greatest length. 49 50 55 Morphol. axis. 44 435 48 Percentage value of Height. 35-2 425 38-5 Actinostome. Long. 443 48-5 39 Morphol- 454 48-5 372 Abactinal area. 236 255 20-8 Anal area. 84 103 7-7 ECHINOMETRA. The characters of the different parts of the buccal apparatus seem here, as in so many other genera of regular Echinoidea, to present just those slight differences in detail which are so important an aid in the accurate discrimination of species. The alveolar foramen, never large, is larger in E. vanBrunti and E. viridis (where it is nearly half as long as the whole alveolus), than it is in E. lucunter or E. suBangularis (where it is very distinctly less than half the length) ; it is smallest in E. lucunter. The radius is simplest in E. lucunter, widening only very gradually and very slowly, and not having its free end notched ; in E. vanBrunti it is a little longer, distinctly wider, but only faintly notched. In E. viridis and E. suBangularis the free end is wider; and in E. suBangularis it is hammer-shaped, owing to its somewhat sudden widening out at its free end; hut there is only a feebly developed notch. In E. viridis the notch is more distinct than in any of the three just mentioned species. When the observer looks straight through the alveolar foramen, holding the tooth vertically, a delicate ascending and descending process on either side is to be observed in E. vanBrunti; in E. lucunter the ascending process can just be detected ; in E. suBangularis neither process can be seen; while in E. viridis it is the descending, instead of the ascending, process which is visible. 1 This species would seem to be figured in the Phil. Trans, vol. xlix. (1755), pi. viii. fig. 3. |