PLUMATELLA DIFFUSA. 105 



tubes are loaded with elongated ova, whicli lie quite loose within them, and are liberated on 

 their rupture ; besides these bodies, we find here also, as in Alcyonella Benedeni, ova of a 

 broadly elliptical shape and imperfectly developed annulus ; these last are always attached 

 firmly to the walls of the tube. P. emarginata admits of an interesting comparison with 

 Alcyonella Benedeni, to which it seems to be related exactly as P. repens is with 

 A. fanyosa. 



8. Plumatella diffusa, Leidy. 



Specific character. — Coencecium adherent, creeping ; cells '" keg-shaped" towards the 

 orifices, which are rendered emarginate by a notch-like furrow continued down one side of 

 the cell on a slight keel. Tentacula forty-two. Statoblasts elongated. 



Synonym. — 1851. PhimateUa diffusa. Leidy, Proc. Acad. Nat. Sci. of Philadelphia, vol. v, p. 261. 



Iconography. — No published figure. 



Habitat. — In running water, covering the under surface of submerged stones, and 

 extending over spaces of from one to several square feet. 



Localities. — Schuylkill and Delaware Rivers, Pennsylvania, and the brooks flowing into 

 them. Dr. Leidy. 



Dr. Leidy gives the following more detailed description of this species : 



" Polypidom diverging from a centre over large surfaces, consisting of a series of simple 

 curved branches, from one to two lines long, rising from one another upon the convex side, 

 and attached throughout their length, except at the extremities, from j to | of a line, 

 which are erect, keg-shaped, or a little dilated at the middle, and contracted at the orifices. 

 Border of the orifices deeply emarginate, and continuous with a fissure down the inner or 

 concave side of the branches upon the summit of a slight ridge. Colour dirty ohvaceous 

 brown, with, the erect extremities of the branches yellowish or translucent whitish. 



" Polypi with forty-two divergent sigmoid tentacula arranged at the summit in the outline 

 of a reniform disc. Length of the tentacula about f of a line ; colour of stomach 

 greenish-yellow. 



" Ovum (statoblast) with its marginal sheath, semi-oval, i^ of an inch long, -^ of an 

 inch broad. Sheath whitish, translucent, smooth, cellular ; with the aperture on its convex 

 side -^r, of an inch in diameter ; that upon its flat side ^^ of an inch. Ovum (statoblast) 

 lenticular, reddish-brown." 



Plumatella diffusa comes certainly very close to P. emaryinata, the slight dilatation of the 

 cell just below the orifice being the only point in which I can find any valid distinction 

 between the two species. 



14 



