Glass 1. Grinoidea. 



129 



like the barbs of a feather. The dorsal surface is covered all over, 

 even to the pinnules, with large, thick, calcareous plates, closely set 

 together, forming in each arm a series of vertebra-like joints, and 

 upon the body a calyx, in which the viscera are disposed. All these 



Fig. 86. 



Fig. 85. 



Fig. 85. l.arvEe of Antedon rosacea at various stagea of 

 development. 1 and 2 young free-swimming larvse ; in the 

 latter, considerable portions of the adult skeleton are already 

 deposited. 3 larva shortly after fixation, g gaatrula-mouth, 

 J) pedal disc, r body, s stalk. — After Wyville Thompson. 



Fig. 86. Another species of Antedon {Antedon Eschrichtii) 

 X 4 ; in the sessile condition. — After Levinson. 



ossicles, which make up a considerable portion of the body, are 

 calcifications of the dorsal wall. The stalk, too, is chiefly composed 

 of a series of calcareous joints; the cirrhi, filiform, or rarely root- 

 like or branched processes, frequently arise from it, and contain 

 similar calcifications. In contradistinction to the dorsal, the ventral 

 surface of both body and arms is usually soft and little calcified. 

 The mouth lies centrally (rarely excentrically) on the ventral 

 surface, and a short distance off is the anus at the tip of a 

 small conical tube in one of the inter-radii. Five ciliated furrows, 

 ambulacral grooves, radiate from the mouth, and if only 



