1881.] 



PROF. F. F. BELL ON THE ECHINOMETRID^. 



427 



I give a sliort technical account of the test ia 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 pri- 

 mary tubercles, which rapidly diminish in size from the amhitus to 

 the actinostome ; at the amhitus 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 ac- 

 tinal surface, but very slightly so on the abactinal. Actinostome 

 moderate, actinal cuts slight, auricles rather dehcate, foramen well 

 marked, connecting ridge slight. General colour of the test yellow- 

 ish green ; the tubercles white. Spines? Hah. ? 



The following are the more important measurements. 



Diameter. Height. Actinostoiue. Abactinal area. Anal area. 



42 19 15-5 10 4 



[45-2]' [37-8] [23-8] [9-5] 



Strongylocentrotus drobachiensis. 



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 aUied 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 otjiers taken to the north of Spitzbergen ; Messrs. Hart 

 ' Percentage value. 2 " E. neglectus." 



28* 



