590 THE VOYAGE OF H.M.S. CHALLENGER. 



by Ehrenberg only by the short diagnosis, " Eadiis stellse tribus apice trimcatis." It is 

 probably identical with his figure of Dictyastrum anyulatum (loc. cit.). This latter name I have 

 retained for the similar Porodiscid (above, p. 526), mainly because the genera Dictyastrum and 

 Rhopalodictyum, according to the insufficient diagnosis of Ehrenberg, seem to be identical. 

 (Compare my Monograph, 1862, p. 466.) 



Dimensions. Eadius of each arm 013, basal breadth 0'09, distal breadth 01. 



Habitat. Tropical Pacific, Philippine Sea, Station 200, depth 250 fathoms ; Atlantic (Mexican 

 Gulf Stream). 



3. Rhopalodictyum subacutum, Ehrenberg. 



Rhopalodictyum subacutum, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d.'-Wiss. Berlin, 

 p. 301. 



Arms of equal size and equidistant, club-shaped, three times as long as the diameter of the 

 central disk, which equals the breadth of the thickened distal end ; the latter is armed with a strong 

 pyramidal terminal spine. (The diagnosis of Ehrenberg is " Eadiis stellar tribus, apice cuneatis 

 subacutis.") 



Dimensions. Eadius of the arms 0'2, basal breadth 0'04, distal breadth 0'07. 



Habitat. North Atlantic, surface and various depths ; Greenland ; Mexican Gulf Stream ; 

 Fseroe Channel (John Murray). 



4. Rhopalodictyum bifidum, n. sp. 



Arms of equal size and equidistant, in the distal half forked, twice as long as the diameter of the 

 tral disk ; both fork branches half as broad as 

 Dimensions. Eadius of the arms 016, basal t 

 Habitat. North Pacific, Station 237, surface. 



central disk ; both fork branches half as broad as the simple basal part,' truncated at the distal end. 

 Dimensions. Eadius of the arms 016, basal breadth 0'08, distal breadth 0'04. 



Subgenus 2. Triactinosphcera, Dunikowski, 1882, Denkschr. d. k. Akad. d. 

 Wiss. Wien, vol. 45, ii. p. 192. 



Definition. Triangular shell bilateral or irregular, with three arms of different size 

 or distance. 



5. Rhopalodictyum zittelii, Haeckel. 



Triadinosphcerazittelii, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, vol. 45, ii. p. 192. 



Arms of different size and at unequal distances, one odd arm being a little shorter than the two 

 paired arms; the odd angle between the latter is larger than the paired angles between them and the 



