ORDER ABRANCHIA. 33 



Blainville thinks that the difference arises from its liaving been 

 confounded with a nearly-allied species, the Black Leech^ 

 which he makes the type of a genus that he calls PsEUDOB- 

 1>ELLA, and of which the jaws are merely folds of the skin 

 without any teeth. I believe this fact would deserve a fresh 

 investigation. Both species devour Lunihrici with avidity. 



Bdella, Sav.^hoxe but eight eyes, and the mouth is com- 

 pletely destitute of teeth. M. Moquin-Tandon changes this 

 name into Limnatis. 



There is one in the Nile, Bel. Nilotica, Egg. Annel. pi. v. 

 f. 4. 



Nephelis, Sav., have also but eight eyes, and their mouth 

 internally has but three folds of the skin. M. de Blainville 

 names them Erpobdell^, and M. Oken Helluo. Such 

 are Hir. vulgaris, L , or H. octoculata, Bergm., Mem. de 

 Stockh. 1767, pi. vi. f. 5 — 8 ; N. atomaria, Caren. L. C. pi. 

 xii. See also pi. vi. of M. Moquin-Tandon. 



There are many small species in our waters, among which 

 we distinguish 'YvMQ.iAW£\k,T)utrocliet, Geobdella, Blainv., 

 which differ only by an enlargement at the seat of the genital 

 organs. 



We have one species of them, which frequently comes to 

 land to pursue the lumbrici, Geobdella trochetil, Blainv. 

 Diet, des Sc. Nat. Hirud. pi. iv. f. 6. 



M. Moquin Tandon, under the name of AuLASTOMA, de- 

 scribes a subgenus whose mouth is also furnished with nothing 

 but longitudinal folds tolerably numerous, Aulast. nigrescens, 

 Moq. Tand. pL vi. f. 4. 



After Nephelis are placed the Branchiobdella, of M. 

 Odier, remarkable for jaws, two in number, and the absence 

 of eyes. 



One species is known, which lives on the gills of the astaci. 

 Brancliiohdella astaci, Od. Mem. de la Soc. d'Hist. Nat. de 

 Paris, torn. i. pi. iv. 



VOL. XIII. D 



