189.').] NATURAL SCIENCES OF PHILADELPHIA. 421 



The four species of Branchiobdella here considered agree with one 



another, and differ from the European species (B. varians of Voigt 

 = B. astaci Odier, -f parasita Braun, + pentodonta Whitman, ,-f 

 hexodonta Gruber) in the possession of two pairs of vasa deferentia, 

 in the fifth and sixth post-cephalic segments; while B. variens, as 

 described by Dorner, whose account I have not seen corrected, has 

 hut one pair. 



Our four species group themselves somewhat naturally in pairs. B. 

 philadelphica and B. illuminata agree in the terete cross-section of the 

 body, the posteriorly directed posterior sucker, the common external 

 opening by means of a vesicle (which is pulsatile in />'. phila- 

 delphica, at least) of the anterior pair of nephridia, and the unlike 

 form of the dorsal and ventral jaws. B. pulcherrima and B. 

 instabilia agree in having the body depressed and more or less laterally 

 expanded posteriorly, in the ventral direction of the face of the 

 sucker, the distinct external openings of the anterior two nephridia, 

 and the similar dorsal and ventral jaws. The second group is much 

 more closely allied to the European forms. 

 Branchiobdella illuminata, sp. nov. 



Fig. la., Plate XII, external outline of the animal of its usual 

 resting form, showing also the outline of the alimentary canal, the 

 principal trunks of the vascular system, the series of clear glands of 

 the right side, and the common nephridia] vesicle opening to the 

 exterior on the dorsum of the third post-cephalic segment, x2M. drawn 

 from a living pecimen. Fig. 16, the two jaws in normal relative 

 positions, x400. Fig. le, outline of a cocoon, x45. 



This species has been named illuminata in allusion to the double 

 series of clear glands which in mounted specimens viewed by trans- 

 mitted light appear like rows of pale-lighted lamps. 



Body very slender in complete extension, but robust in contrac- 

 tion, tapering from the seventh segment very gently toward the head, 

 and suddenly to the posterior sucker ; terete in transverse section in 

 all regions. P>i- aim illation of segments very conspicuous throughout 

 the entire length. Posterior sucker small and weak, on the same 

 axis as the body segment. Head small, slender, and elongated ; the 

 post-oral part distinctly bi-annulate. Lips long and weak, of uearlv 

 equal size ; ridged within by longitudinal folds. Mouth opening 

 with its longest diameter transverse. No circmnoral or other hairs 

 have been detected in the adults of this species; and in the young a 



