OCR Text |
Show 1881.] PROF. F. F. BELL ON THE ECHINOMETRIDsE. 427 I give a short technical account of the test in question, together with the more important measurements. Test somewhat depressed; apical system large ; genital pores large ; two large oculars touch the periproct; pairs of pores five in an arc ; in one or two cases there are six ; the lowermost pair is separated from and is internal to the rest, so that it forms a well-marked inner line. On each series of the plates of the corona there is a row of large primary tubercles, which rapidly diminish in size from the ambitus to the actinostome ; at the ambitus the interambulacral tubercles have a smaller primary on either side; the outermost of these rows reaches to the actinostome, and extends also a short way up the side of the test; the inner row extends higher up the side of the test, but soon becomes lost on the actinal surface; the ambulacral plates are well provided with secondary and miliary tubercles on the actinal surface, but very slightly so on the abactinal. Actinostome moderate, actinal cuts slight, auricles rather delicate, foramen well marked, connecting ridge slight. General colour of the test yellowish green ; the tubercles white. Spines? Hab.? The following are the more important measurements. iameter. 42 Height. 19 [45-2]' Actinostome. 15-5 [37-8] Abactinal area. 10 [23-8] Anal area 4 [9-5] STRONGYLOCENTROTUS DROBACHIENSIS. Absolute diameter, in millim. 11 12 19 24 30 35 39 532 (?)65 Percentage value of Height. 63-63 50 50 45-8 43-3 42-8 512 566 58-4 Actinostome. 45-45 43-7 47 41-6 41-6 38-5 38-4 35-8 30-7 Abactinal area. 263 27-08 30 25-7 25-6 22-6 18-4 Anal area. 1818 22-7 1315 14-5 15 15 12-8 13-2 10-7 Some of the fluctuations in percentage values shown by the above table give an idea of the variations exhibited by this widely spread and circumpolar species. The author of the ' Revision of the Echini' rendered considerable service to the students of this and allied species, when he pointed out that under the name of S. droBachiensis it was necessary to include so many that are merely nominal. Mr. Leigh Smith has presented to the British Museum specimens of this species which he dredged in the seas off Franz-Joseph Land, as well as others taken to the north of Spitzbergen; Messrs. Hart 1 Percentage value. 2 " E. neglectus." 28* |