Miscellaneous. 243 



P. gracilis, nigricans, lateribus parallelis, postero acuto abrupte, ple- 

 rumque antico recto ; oculis duobus. Long. 9 lin., lat. 1 lin. Habi- 

 tat in fontibus Pennsylvanise. 



Description. Oblong, limaciform, naked, convex superiorly, flat in- 

 feriorly, very contractile ; sides ordinarily parallel, convex when the 

 animal is in a contracted state, convergent anteriorly when elon- 

 gated ; anterior extremity with a lateral triangular auricular appen- 

 dage, straight in front, by contraction becoming convex or concave ; 

 posterior extremity abruptly pointed ; ocelli two, anterior, composed 

 of an oblong, semitransparent (nervous ?) mass with an intensely 

 black dot of pigmentum at the internal posterior part ; ventral aper- 

 tures two ; oral aperture a little less than one-third the length of the 

 body from the posterior extremity, and very dilatable ; generative 

 aperture half-way between the oral aperture and posterior extremity. 

 Colour black or iron gray, and in some younger specimens lateri- 

 ceous. 



This animal I have only found in abundance in the neighbourhood 

 of Prof. Haldeman's residence, near Columbia, Pa. In a spring in 

 front of his house, thousands of them may be seen gliding along the 

 bottom ; some of them occasionally creep up the sides to the surface 

 of the water, turn upon the back, and by making the ventral surface 

 concave, float about in the manner of the Limniadce. It appears to 

 be carnivorous in habit, or at least it attaches itself to animal matter 

 dead or living, in preference to vegetable matter. When irritated, 

 it throws out a considerable quantity of very tenacious mucus. 



In structure it appears to be intermediate between the entozoic 

 Distomata and the annulose Hirudince. I could not detect any trace 

 of annulation, but I think that this alone would hardly be sufficient 

 to place it lower than the latter animals, because, in a closely 

 allied animal, the Gordius aquaticus, although there is no annulation 

 in the perfect animal, yet in the embryo state I find it to exist. 



The whole animal is composed of a delicate granular structure ; 

 the only approach to muscular fibre is in the longitudinal striation of 

 the integument rendered more distinct by the pigmentum nigrum, a 

 radiated appearance around the oral orifice, and a faint transverse 

 and longitudinal arrangement of the granules entering into the com- 

 position of the proboscides, seen more or less distinctly in the con- 

 tinued movement of these organs when slightly compressed beneath 

 the microscope. 



The digestive cavity presents the same dendritic arrangement as 

 in Planaria generally*, but instead of possessing a single sucker or 

 proboscis, the full-grown animal has not less than twenty-three ; 

 varying however in this respect from three upwards, according to the 

 age of the animal. One of these proboscides joins the digestive cavity 

 at the posterior part of the anterior division, as usual ; the others join 

 the remaining two divisions at their internal side in their course 

 backwards. They are considerably longer, but narrower, than in P. 

 lacteaf, and when not in use are closely packed together within the 



* Dug^s, Ann. So. Nat. t lb. 



16* 



