ECHINUS. 261 



elegans, while another (armaius), the relationships of which are doubtful, was 

 taken by the "Siboga" in the East Indies. The remaining species are all from 

 the southern hemisphere. Two {Gilchrisli from South Africa and anchistus, from 

 deep water off the coast of Chile) are very near to some forms of acutus, though 

 now so widely separated geographically. Other southern species are horridus 

 and euryporus from "Challenger" Station 308, off the coast of Chile, in 175 

 fathoms. Doderlein has recorded horridus from off South Africa also, and a 

 young specimen from off St. Paul Island still further to the east: the latter 

 individual is so small that its identification seems very doubtful. The most 

 characteristic of the southern species is margaritaceus, which appears to have 

 a wide distribution in the Antarctic Ocean. 



The status of many of these species is open to question, due no doubt, in 

 part at least, to the lack of material. It is probable that knowledge of the color 

 in life would help in determining the true position of some forms. There seems 

 to be a general and justified feeling of doubt as to whether melo is specifically 

 different from acuius. It has seemed best however, to retain melo for the present 

 as few specimens are available and those are quite easily recognizable. The 

 similarities between Alexandri and elegans are striking and lucidus is \'ery near 

 indeed to the latter. One has to search very carefully for any differences what- 

 ever between these three species and all found seem exceedingh' trivial. ^lore- 

 over the three are very near some forms of acuius var. norvegicus. Typical 

 acutus, when full grown, is so very different from norvegicus that it was hard to 

 accept Mortensen's claim that they are identical, but examination of a large 

 series of specimens shows that it is not practicable to draw the line between 

 the two forms. It is necessary however to go still further for affinis is not 

 distinguished from norvegicus by any constant characters; the one is simpl}' the 

 most highly specialized form of the other. This form (affinis) is remarkable 

 for the frequency with which the uppermost ambulacral plates have only two 

 elements, as noted and figured by Jackson (1912, iVIem. Boston Soc. Nat. Hist., 

 VII, p. 118, text-fig. 115). 



There is no question about the validity of esculenttis and ]\Iortensen's descrip- 

 tion of tenuispinus would indicate the desirability of accepting that species. 

 There is no doubt about the standing of gracilis and atlanticus, which are \Try 

 distinct and easily recognized species, and the same is true of tylodcs. I 

 consider Wallisii as somewhat doubtful as it may be simply the full-grown adult 

 of Alexandri; the smallest TTa/Zisu is 60 mm. h. d. while tlie largest Alexandri is 

 only 50 mm. The test in Wallisii is so thick and rough, that it is hard to believe 



