262 HAWAIIAN AND OTHER PACIFIC ECHINI. 



that Alexandri would reach such a condition, even with a great increase in size. 

 As de Meijere's description of armatus fails to make clear the character of either 

 the buccal membrane or the abactinal system, its true position is doubtful. 

 It appears to be a connecting link between Echinus and Heliocidaris, having 

 the ambulacra of the former, with the globiferous pedicellarise of the latter. 

 Although, as already stated, Gilchristi and anchistus are near some forms of acutus 

 (notably affinis), they seem to be valid species and the same may be true of 

 euryporus, but it is very difficult to separate the last from elegans in any satis- 

 factory way. More material is greatly needed for the elucidation of horridus; 

 the specimen from South Africa figured by Doderlein seems to be identical with 

 the "Challenger" specimens. One of the latter, the only specimen accessible, 

 is very remarkable for the form of the test; although when collected it was 

 broken into a number of pieces, some of which are missing, there is no question 

 that in life the vertical diameter greatly exceeded the horizontal, and so far as it 

 can be estimated, must have been nearly twice as much. Such a high test has 

 not hitherto been recorded among Echini either living or fossil. 



As regards margaritaceus, I disagree with the eminent Continental zoologists 

 who make it the type of a genus Sterechinus, in which they recognize 

 four species (margaritaceus, Neumayeri, antarcticus, diademd). Although the 

 material studied is not extensive, it is very representative, consisting of speci- 

 mens from Patagonia, Kerguelen, Heard Island, Coulman Island, "Gauss" 

 winter station, and Antarctica (Mission Charcot), and including specimens 

 identified by Koshler as Neumayeri and by Mortensen as diadema, antarcticus, 

 and Neumayeri. Although these specimens reveal a certain amount of diversity, 

 it is not nearly so great as that shown by acutus or by our common northern 

 sea-urchin, Strong ylocentrotus drobachiensis. Moreover the differences are not 

 only slight but are very inconstant and it seems unwise to distinguish more than 

 a single species. Owing to the characteristic form and appearance, and particu- 

 larly the specialized abactinal system, it would have been advantageous to 

 recognize the genus Sterechinus (see below under Evechinus) but horridus is 

 such an obvious connecting link in certain particulars, though so different in 

 others, and the resemblance to esculentus in ambulacra and buccal plates is so 

 noteworthy that margaritaceus cannot be removed from Echinus. 



The species of Echinus which seem valid may be distinguished as follows, 

 although in some cases the general appearance is of more value than the trivial 

 characters here used. Attention should be called to the fact that acutus occurs 

 in two places in the table owing to its variable ambulacra. Not having seen 



