PLUMULAEIA FILICULA. 29 



which is obliquely cut above and below so as to present two broad 

 lateral teeth. 



Gonosome not known. 



In its opposite hjdrothecte adnate to the axis for only half their 

 height, and disposed in distant pairs, this hydroid has so much of the 

 aspect of a Sertularia that it might at first sight be easily referred 

 to that genus. The fact, however, that the pairs of hydrotheca? are not 

 separated from one another by a joint removes it from Sertularia, and 

 notwithstanding the freedom of the hydrothecse for so considerable a 

 portion of their height, brings it into the genus Thuiaria.* 



It is a slender form, with a somewhat rigid habit which it would seem 

 to owe to the non-jointed condition of the axis. 



Family PLUMULARIDiE. 



Genus PLUMULARIA, Lamarck (in part). 



Plumularia filicula. 

 PL XV III. Figs. 1, 2. 



Trophosome. — Hydrocaulus attaining a height of about two inches, simple 

 or with an occasional branch close to the root, not fascicled ; pinna) alter- 

 nate, one borne by each internode of the stem, immediately below a joint, 

 where it is supported on a long process of the internode ; proximal inter- 

 node of thepinnsB short and destitute of hydrotheca; following internodes 

 elongate, every alternate one carrying a hydrotheca, the hydrotheca-bearing 

 internodes slightly longer than the intervening ones. Hydrotheca3 small, 

 each borne near the middle of its supporting internode. Supracalycine 

 nematophores large ; a single mesial nematophore borne by the hydrothecal 

 internode at the proximal side of the hydrotheca, two by each of the inter- 

 vening internodes, and a single one by the short proximal internode. 



Gonosome. — Gonangia elongate, oval, smooth, narrowed below into a 



* I regard the presence of a joint at regular, intervals between every two or every two pairs of hydro- 

 thecEe as an essential character of the true Sertularidans (_ Sertularia, Sertularella, Diphasia) quite irrespec- 

 tively of the extent to which the hydrothecae are adnate to the hydrocaulus. In Thuiaria, on the other 

 hand, the joints occur at distant, and for the most part irregular intervals, thus allowing numerous hy- 

 drotheca to follow one another without any intervening joint. See Journ. Linn. Soc. Zoology, Vol. XII. 

 p. 267. 



