OF THE 'POECTJPmE' EXPEDITIONS. 475 



also brought up in dredgings made outside of this region in depths of 203 and 

 290 fathoms, with temperatures of 47°'6 Fahr. and 41°-5 Fahr. 



PLUMULARID^. 



Among the eight genera to which the new hydroid species of the expeditions may be 

 referred, no less than four belong to the family of the Plumularidae — a family in 

 which the dredgings were especialy rich, both in new species and in species which had 

 been already described. Among the species now for the first time made known, are 

 several highly interesting forms, which not only render necessary the construction of 

 some new generic groups, but suggest the modification of some old ones. 



I propose to distribute the new Plumularidae of the ' Porcupine ' expeditions under the 

 following four genera — Aglaoplienia, HaUcornaria, Cladocarpus, and Biplopteron. 



Aglaophenia. 



The genus Aglaophenia is here understood in a somewhat restricted sense, and must 

 be regarded as limited by the following diagnosis : — 



Trophosome. — Hydrocaulus with pinnate ramification. Hydrothecse usually with an 

 intrathecal ridge. Nematophores fixed ; lateral nematophores one on each side of the 

 orifice of the hydrotheca ; mesial nematophores adnate for a greater or less extent to 

 the front of the hydrotheca. 



Gonosome. — Gonangia included in corbulae, each of which replaces an ordinary pinna. 



The presence of an intrathecal ridge, referred to in the above diagnosis, affords a 

 character hitherto overlooked in the descriptive zoology of the Plumularidse. I have 

 given this designation to a more or less obliquely transverse ridge, which occurs in the 

 interior of the hydrothecse of a large number of Plumularidse, where it forms an imperfect 

 septum, by which the hydrotheca becomes divided into a proximal and a distal portion. 

 The form of this ridge varies, and will afl'ord characters available in specific diagnosis. 



Aglaophenia dromaius. Plate LXVII. figs. 1, 1°, 1*, 1°. 



Trophosome. — Stem attaining a height of between five and six inches, simple, flexUe, 

 slender, not fascicled, divided into internodes of equal length ; pinnae springing each from 

 a point near the middle of an intemode, alternate, rather distant, of nearly equal length, 

 extending along the stem to within a short distance of its base. Hydrothecse deeply 

 concave in front just above the line of attachment of the mesial nematophore ; margin 

 deeply toothed ; intrathecal ridge strong, commencing at the front of the hydrotheca just 

 below the orifice by which the cavity of the mesial nematophore communicates with that 

 of the hydrotheca, and thence extending backwards but not meeting the mesial line of the 

 back ; mesial nematophore adnate for about two thirds of its length to the front of the 

 hydrotheca ; lateral nematophores of moderate size, slightlj- overtopping the hydrotheca. 



