54 THE VOYAGE OF H.M.8. CHALLENGED. 



Gonosohic. — Gonangiu springiiig from the stem, and destitute of special protective 

 apparatus. 



The geuus Azyyoplon is essentially cliaracterised liy the veiy exceptional condition 

 of having no lateral nematophores — a condition which, except in DqAocheihis, does not 

 occur elsewhere among the known genera of riumularidte. So far as is yet known, 

 Azygoijloii is represented l)y one species only. 



Azygoplon rostratum, n. sp. (PL XIX. figs. 1-3). 



Trophosome. — Colony attaining a height of upwards of three inches ; stem much and 

 irregularly branched, monosiphonic ; hydi'ocladia about two-tenths of an inch in length. 

 Hydrothecse rather shallow, with one strong marginal tooth on each side, and a long 

 beak-like j^i'ocess in front ; mesial nematophore adnate for its entire length to the 

 anterior wall of the hydrothcca, and then bearing on its summit a free membranous 

 scoop-shaped appendage. 



Gonosome. — Gonangium nearly spherical, narrowed into a .short .stalk at its point of 

 attachment to the stem close to the base of a hydrocladium. 



This is a very remarkable Hydroid. The form of the hydrotheca is exceptionally 

 striking, for instead of the serrated margin usual in the Statoplean Plumularidaj, this 

 condition is here replaced by a single strong tooth on each side and a long beak-like 

 projection of the margin in front. The mesial nematophore — the only one }iresent in the 

 genus — is divided into two portions bj' a transverse joint ; the proximal portion is the 

 proper nematophore, and is, as in the mesial nematophore of other Statoplean forms, a. 

 simple continuous projection of the hydrothecal internode, and is adnate for its entire 

 length to the anterior walls of the lu'drotheca ; the distal portion consists of a free 

 membrane bent into a scoop-shaped form, the concavity of which is turned towards the 

 hydrotheca and embraces its anterior wall. 



The stem is divided into iuternodes by transverse joints, and every internode gives off 

 from alternate sides a hydrocladium. The joints by which the internodes of the hydro- 

 cladia are separated from one another are unusually well marked — a feature in which 

 Azygoplon rostratum approaches the Eleutheroplean rather than the Statoplean forms. 



The specimen had l)een broken away from its hydrorhizal end, and on this account 

 no exact assertion can lie made of the height which the species may attain. 



Azijgoploii rostratum comes very near to a species described and figured ])y Kirchcn- 

 pauer under the name of Aglaophenia avicidaris, from specimens brought from Bass 

 Strait. If it were not for the very diiferent firm of the mesial nematophore, I .should 

 have regarded the Challenger species as identical with that of Kii'chenpauer. 



Dredged at Station 161, April 1, 1874, off the entrance to Port Philip; depth, 38 

 fathoms ; bottom, sandy. 



