REPORT ON THE HYDROIDA. 33 



two series of pinnately-disposed, alternate, free ribs, each rib carrying near its base a 

 hydrotheca. Gonangia springing from tlie racliis. 



The remarkable mode in which the branches oi Acantliodadiuin terminate, recalls the 

 very similar condition presented by the genus Aecuithella ; but while Acanthocladium is 

 a Statoplean form, Acanthella belongs to the Eleutheroplea, The gonosome of Acantliella 

 is unknown, but the specimens of Acanthocladium liuxleyl the only species of the 

 genus as yet discovered, are, on the contrary, abundantly provided with this important 

 element of the colony. The phylactocarp of Acanthocladium belongs to the same type 

 as that of the Aglaophenia dida)is and Aglaoijhenia hisjnnosa of the Gulf Stream Eeport,^ 

 every rib carrying, as in these last, near its base a modified hydrotheca. The distal portion 

 of the rib is in all these cases the greatly modified mesial nematophore of this hydrotheca, 

 while the proximal portion is a peduncle which springs from the rachis and supports the 

 modified hydrotheca and its appendages. {See p. 11). 



Acanthocladium huxleyi, Busk, sp. (Pis. IX. and XX. figs. 1-3). 



Plumidaria Jiuxleiji, Busk, Voyage of tlie "Rattlesnake," vol. i. p. 395, 1852. 



Trophosome. — Colony attaining a height of fifteen inches ; stem fascicled, springing from 

 a dense cushion of fine entangled tubes, undulated, giving oflf pinnately-disposed alternate 

 simple branches about two inches in length, which carry the hycbocladia and terminate each 

 in a jointed prolongation which is composed of numerous (twelve to sixteen) internodes, 

 every internode carrying a slightly curved spine, which is supported on the extremity of 

 a short process from alternate sides of the internode, and carries two rows of small cup- 

 shaped nematophores ; hydrocladia alternate, short, about one-tenth of an inch in length. 

 Hydrotheca3 approximated, wide and rather shallow, with an anterior parietal fold and a 

 very short intrathecal ridge ; orifice of hydrotheca with its plane parallel to the axis of 

 the short internode, margin crenate ; mesial nematophore adnate to the entire height of 

 the hydrotheca wall, and then continued as a long, free, curved spine which arches over the 

 orifice of the hydrotheca ; lateral nematophores short, crescentic. 



Gonosome. — Phylactocarps developed in a continuous series on each side of the 

 branches near their middle, every series having the unmodified hydrocladia at its proximal 

 and usually also at its distal side ; costas of phylactocarp twenty-six to thirty in numljer 

 springing alternately from the sides of the rachis, over Avliich they arch, each carrying a 

 double row of cup-shaped nematophores, and at about one-third of its length from the 

 base, a single small deep hydrotheca. Gonangia ovoid, springing from the rachis, each 

 close to the origin of a costa. 



The long fiexile undulating stem and simple plume-like branches of Acanthocladium 



1 Albuan, Report on the II ydrokla collected during the exploration of tlie Gulf Stream, by L. F. De Pourtales, United 

 States Coast Survey, 1877, p. 44, pi. xxvi. figs. 1-8, and p. 46, pis. xxvii., xxviii. 



(ZOOL. CHALL. EXP.— PART X.X. — 1883.) U 5 



