ECHINOIDEA. II. 



larger specimen (130") I count 7 8 such plates in each series, all being provided with a pore. Of 

 the inner plate without pore" no trace is seen, and since there is otherwise such a plate for each three 

 pore-bearing plates, this fact must mean that the poreless plate becomes absorbed on passing to the 

 buccal membrane. On the abactinal side it is seen that the larger primary plate is from the beginning 

 undivided; but already from the third or fourth the dividing line has appeared, though not easily 

 discernible before nearer to the ambitus. All the pores are distinct, only that of the inner small plate 

 distinctly the larger, corresponding to the larger size of the tubefoot of this plate. 



Fig. 27. Part of the actinal and abactinal side of the test of Sperosoma Grimaldi; 



The genital and ocular plates are already separated by small anal plates, except the ocular 

 plate III which is still in contact with the adjoining genital plates. In younger stages the apical 

 plates will undoubtedly form a closed ring. The genital pores have not yet appeared; in a specimen 

 of 4o mm diameter from the Fseroe Channel they have appeared, but the genital organs are still very 

 small. The ocular plates are rather large, with a peculiar radiating striation in the outer part. The 

 anal area is closely covered by numerous small plates, those at the outer edge being somewhat larger; 

 the inner ones are narrow and elongated, radially arranged round the anal opening. - The gills 

 have not yet appeared in this specimen, but in the specimen of 40'" they are present, though still 

 very small. 



This species was taken by the Thor at 62 57' Lat. N. 19 58' Long. W. 957 M. in 1903 and at 

 61 15' Lat. N. 9 35' Long. W. 900 M. in 1904. 



22* 



