AMONG THE SEA URCHINS. 261 



St. Anne's pier the larval form of this curious Holothurian. This 

 larva, for which at first we had some difficulty in finding a name 

 and description, is a most interesting microscopic object, moving 

 across the zoophyte trough with a curious gliding motion, evidently 

 caused by the action of the cilia with which it is encircled. Our 

 digging exertions, though unsuccessful in our main object, were, 

 however, rewarded with turning up many of our old friends, the 

 sea-eggs {Echinocardium cordatti?n), with their hair-like spines 

 moving in every direction. Especially noticeable were the strong, 

 spoon-shaped spines with which they can so quickly hide them- 

 selves under the sand. These Urchins, like the rest of the 

 Spatangidce family, have no teeth, the large mouth-opening being 

 contracted by a buccal membrane, through which the creature 

 sucks in the sand, from which it extracts minute particles of food, 

 passing the sand through its intestine in a manner very similar to 

 that of the earth-worm, and discharging it from the " periproct,' 

 which is high up in the posterior, just above a most curious 

 plastron, or ornamental space, surrounded by a " fascicle " of tiny 

 spines. There is another fascicle or granular band of close-set, 

 tiny spines and pedicellariae on the upper side of the shell, which^ 

 though ornamental, is not so distinctive as the fascicle forming the 

 " Fiddle " on Brissopsis larifera (PI. L, Fig. i). There is no doubt 

 that these fascicles act as screens to prevent refuse from interfering 

 with the action of the tube feet. 



Since our article in January last, we have been at considerable 

 trouble to look through the bibliography of the Echini, especially 

 those of foreign authors, and although the calcareous rosette shown 

 in PI. L, Fig. 2, is often referred to and fully described, as well as 

 the spicules, we found it is only illustrated by single plates, as in 

 Fig. 3. We have, therefore, thought the structure so beautiful as 

 to be deserving of a more elaborate drawing, which is presented 

 in PI. XVIIL, Fig. 1. This calcareous disc of the pedicel or 

 sucker-foot consists of from four to eight wedge-shaped plates,* 

 riddled with holes, the outer edge of which, though beautifully 



* Agassiz states that the sucker-discshave only four plates {vide "Revision 

 of the Echini," 1874, p. 700). The greatest number of specimens examined by 

 us had six plates ; from our preparation of one of these our illustration was 

 drawn. 



