or THE 'PORCUPINE' EXPEDITIONS. 479 



dichotomously branched, provided with numerous nematophores along their length, and 

 cariying the gonangia singly at the points of bifurcation ; a gonangium is also frequently 

 borne by the main stem close to the origin of a pinna. Gonangia (sex indeterminable 

 in the specimens) nearly sessile, obovate. 



This very beautiful species was dredged from a depth of 167 fathoms, where the tem- 

 perature of the bottom stood at 44°'3 Fahr. 



DiPLOPTERO'. Gen. Char. 



Trophosome. — Hydrocaulus plumose, doubly pinnate, nematophores movable, never 

 adnate to the hydrotheca; hydrothecse destitute of intrathecal ridge; two pairs of 

 lateral nematophores flanking the hydrotheca. 



Gonosome. — Gonangia not protected by corbulae or by special ramuli. 



The genus Diplopteron is distinguished from Plumulana by its doubly pinnate rami- 

 fication, and by the possession of two pairs of lateral nematophores. The doubly pinnate 

 hydrocaulus of Dijjlopteron confers upon this genus a very striking and instantly reco g- 

 nizable feature, which marks it out from Plumulana as distinctly as Antennularia is 

 distinguished from the same genus by its verticUlate ramification. ., 



We know of no other member of the family in which there is more than a single pair 

 of lateral nematophores. 



DiPLOPTERON INSIGNE. Plate LXVIII. figs. 2, 2", 2\ 2'. 



Trophosome. — Stem attaining a height of about 6 inches, giving oflF an occasional 

 branch, rooted by an entangled mass of tubular filaments, and carrying closely set, regular, 

 opposite, primary pinnae, which are destitute of hydrothecse,' and carry along their entire 

 length the ultimate or hydrotheca-bearing pinnae ; stem and primary pinnae fascicled, 

 becoming single only towards the distal extremities ; ultimate pinnae borne not only on 

 the primary pinnae but on the stem, in the intervals between the primary pinnae, closely 

 set, alternate, and of nearly equal length, divided by oblique joints into internodes, and 

 giving off each close to its origin a branchlet, which often bifurcates. Hydrothecae deep, 

 bell-shaped, free for about the distal half of their length, orifice circular, entire, slightly 

 everted, every intemode of the ultimate pinnae carrying a hydrotheca. Two very large 

 bithalamic lateral nematophores borne on each side of the hydrotheca and there articulated 

 to a lateral process of the intemode, while a pair- of minute lateral nematophores is carried 

 just above them, a mesial nematophore borne by the intemode at the proximal side of 

 the hydrotheca and another at its distal side. 



Gonosome. — Gonangia oval, with truncated summit, borne on a short two-jointed 

 peduncle, which springs from the ultimate pinna close to its origin. 



In the opposite disposition of the jjrimary pinnae of Diplopteron insigne we are 

 reminded of the ramification of Plumularia catharina. In this Hydroid, however, the 



3x2 - 



