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 Hehocidaris, having 

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

 Although, as already stated, Gilchristi and anchisius 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, antardiciis, diadema). Although the 

 material studied is not extensive, it is \'ery representative, consisting of speci- 

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

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

 identified by Koehler 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 bj- acutus or by our common northern 

 sea-urchin, Strong ylocentrot us drobachiensis. MorcoNcr the differences are not 

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

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

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

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

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

 otluMs, and the reseml)lance to cscuhntus in ambulacra and buccal plates is so 

 notewortliy that margaritncciis cannot be removed from Echinus. 



Tiie species of iM-hinus which seem valid may be distinguished as follows, 

 although in some cjises tiie general apjiearance 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 



