CHAP. IV.] THE CR VISES OF THE ' PORCUPINE: 157 



rows of tube feet, its spines, and five sharp blue teeth ; 

 and curious undulations were passing through its 

 perfectly flexible leather-like test. I had to summon 

 up some resolution before taking the weird little 

 monster in my hand, and congratulating myself on 

 the most interesting addition to my favourite family 

 which had been made for many a day. 



Calveria hystrix — for I have named this genus and 

 species after our excellent Commander and his tidy 



I''iG. 28. — Calveria hystrix, WvviLLE Thomson. Inner sui-face of a portion of the test showing 

 the structure of the anibulacral and interambulacral areas. 



little vessel, in grateful commemoration of the plea- 

 sant times we had together — is circular and depressed, 

 rather more than 120 mm. in diameter, and about 

 25 mm. high (Fig. 28). Both interambulacral and 

 ambulacral areas are wide. The peristome and the 

 periproct are unusually large ; the former covered with 

 calcareous scale-like plates, perforated up to the rim of 

 the mouth for the passage of ambulacral tube-feet, as 

 in Cidaris; the latter with a large madreporic tubercle 



