ECHINOIDEA. II. 



171 



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

 tlie iiiiier plate without pore 110 trace is seen, and since there is otherwise such a plate for each three 

 pore-bearing piates, this faet must mean that the poreless plate becomes absorbed on passing to tlie 

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

 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 aud abactinal side of the test of Sperosoma Grimaldi; 2-]^'". 



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

 plate III whicli is still in contact with the adjoining genital piates. In younger stages the apical 

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

 of 40'"™ diameter from the Færoe Channel they have appeared, but the genital organs are still very 

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

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

 the inner ones are narrow and elongated, radially arranged rotmd the anal opening. — The gills 

 have not yet aj^peared in this specimen, but in the specimen of 40""" thev 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. 



