148 Rev. T. Hincks on the Hydroida. 



XII. — Contributions to the History of the Hydroida. 

 By the Eev. Thomas Hincks, B.A., F.R.S. 



[Plate XII.] 



I, New British Species. 

 Subcider THECAPHORA, Hincks. 



Family PlumulariidsB. 



Genus Plumularia, Lamk. (in part). 

 Plumularia siliquosa, n. sp. (PI. XII. figs. 2-6.) 



Shoots clustered, simple, not plumous, resembling ordinary 

 pinnse, but rising directly from the creeping stolon and not borne 

 on an erect stem, regularly jointed, the joints oblique : 

 hydrothecce cup-shaped, rather deep, with an even margin, 

 standing out from the shoot, one on each internode immediately 

 above the joint : sarcothecce three on each internode, bithala- 

 mic ; one of them, immediately below the calycle, of larger size, 

 curved, projecting, one above the calycle, and one at the upper 

 extremity of the internode immediately below the joint ; two 

 in connexion with the calycle, one on each side above, pe- 

 dunculate, emarginate on one side : gonothecce (female) elongate, 

 ti-uncate at the top, -and tapering off below ; (male) very small 

 (about ^ the size of the female), ovate, curved inwards, somewhat 

 pointed below. 



This very distinct species was obtained on the coast of 

 Guernsey by R. S. Cooper, Esq., of Weymouth, lately resident 

 at St. Peter's Port, who has paid much attention to the marine 

 zoology of the island, and whose stores of information and 

 material have always been freely placed at the service of his 

 brother naturalists. He has kindly supplied me with the spe- 

 cimens on which the above description is founded. 



P. siliquosa has only occurred so far in the stemless form; 

 but it is probable that in its perfect condition it exhibits the 

 plumous mode of growth which is characteristic of its tribe. 

 P. Catharina is also found occasionally in this humble guise ; 

 but more commonly it assumes the true Plumularian habit. 



The calycle in the present species exhibits no very distinc- 

 tive feature, if we except the pair of pedunculate sarcothecse 

 which are associated with it. These differ from the similar 

 structures on P. Catharina in being emarginate on one side, a 

 peculiarity which also occurs in one at least of the species 



