404 Prof. F. J. Bell on a new Species o/'Evechinus. 



packed and gradually and regularly increasing in size as they 

 pass from the actinostome to the ambitus, where they are not, 

 however, as large as the primary tubercles of the ambulacral 

 area ; between these there is a single row of secondary 

 tubercles. Above the ambitus the primaries rapidly become 

 smaller or completely disappear, and as much as half the 

 abactinal surface of the test may be completely devoid of 

 primary tubercles, when the plates are covered only by small 

 tubercles, not very regularly arranged. 



The auricles are strong, the foramen small, and the con- 

 Be«ting-ridge low. The buccal apparatus is injured, but the 

 radius would appear to have a shallow rounded notch. 



The spines are of moderate length, ' greenish in colour 

 except at their tip, which is yellowish -, a specimen com- 

 pletely covered with spines would probably have very much 

 the same appearance as E. chloroticus (though as compared 

 with most dried specimens the spines are of a darker green), 

 but might be distinguished from it by the greater number of 

 short and the smaller number of long spines. 



The following table gives the more important measure- 

 ments : — 



As E. chloroticus grows to a considerable size, it is of 

 importance to consider whether the diiFerences indicated in 

 the above description are not those of age ; the differences in 

 the proportional size of the actinal and abactinal areas would 

 possibly be less if we had larger specimens of E. rarituher- 

 culaius ; but the character which " leaps to the eyes " is the 

 smaller number of primary tubercles. Fortunately we have 

 already from M. ilex. Agassiz (Rev. Ech. p. 503) some 

 information as to the youthful characters of E, chloroticus^ 

 and he tells us that in specimens 18 millim. in diameter, or 

 only two fifths the size of one of ours, there were already 

 fourteen coronal plates, which is, I presume, equivalent to 



