262 [Skptembkr, 



ginate and continuous with a fiss\ire down the inner or concave side ot t!ie 

 branches, upon the summit of a slight ridge. Colour dirty olivaceous brown, 

 with the erect extremities of the branches yellowish or translucent wliitish. 



Polyp with 42 divergent, sigmoid tentaculae, arranged at their summits in the 

 outline of a reniform. disk. Length of the tentaculas about 3-5ths line. Color of 

 the stomach greenish yellow. 



Ovum with its marginal sheath semi-oval, l-6Sth in. long, l-333d in. broad. 

 Sheath whitish, translucent, smooth, cellular; with the aperture upon its convex 

 side 1-I42d in. in diameter ; that upon the flat side l-133d in. Ovum lenticular, 

 reddish brown. 



Ilahitation. Upon the under surface of stones which do not come in contact 

 entirely with the ground, in running brooks and creeks emptying into the Schuyl- 

 kill and Delaware rivers, and also in the latter. 



Hemarhs. This species of Plumatella appears to prefer for its residence stones 

 of large size. It is not common to find it upon such as are under 3 or 4 inches 

 square, but is frequently seen covering surfaces closely from one to several feet 

 square, upon which I have counted from 150 to 300 polyps to the square inch. It 

 also flourishes best in the course of currents of moderate strength. 



The object of its occupying the under surface of stones appears to be not so 

 much to escape from the light, as it is to favour the removal of the abundant ex- 

 crement, which is voided in the form of oblong, greenish or clay colored pellets. 



The interior structure of Plumatella corresponds pretty closely with those of 

 Alcyonella. 



The extruded ova are frequently found attached to rocks, generally by the flat 

 side, but sometimes by the convex side. 



The sheath of the ovum is composed of transparent colorless cells, about the 

 l-4000th In. diameter. 



Whilst observing this species of Plumatella beneath a lens, 1 noticed 

 several small aquatic larvae, probably of a species of Hydrophilus according 

 to my friend Dr. Le Conte, which would advance the anterior part of the 

 body, up the erect portion of the branches of the polypidom, with all the 

 stealth of a spider, until upon a level with the margin of the orifices, when they 

 would suddenly dart with great rapidity upon the body of the polyps : but in 

 every instance for a quarter of an hour in which I observed them, the latter suc- 

 ceeded in escaping by contracting within the tubes, where the larvte appeared 

 not to be disposed to follow them. 



Dr. Leidy observed that he had for some time past been collecting 

 materials towards elucidating the natural history of the family of Gor- 

 diacese, Siebold, upon which he was now preparing a memoir for the 

 Journal. 



Our most common species has been confounded with the Gordius aquaticus, L., 

 of Europe, but a striking character at once proves it to be distinct. The caudal 

 extremity of the female is trifurcated, while that of the European species is 

 blunt.* The length is from 4 to 12 inches. Of this species there are several 

 varieties from different localities, which may upon further comparison prove to 

 be distinct species. 



To this species the name Gordius varius was proposed. A second species of 



Siebold : Arch. f. Naturg. 1835, p. 303. 



