265 



Obs. Planaria gracilis^ and very likely Planaria tigrina 

 will not remain in the genus Planaria as soon as we shall know 

 their internal structure. 



Dendroccelum pulcherrimum Girard. The largest species 

 of that family hitherto known in the fresh waters of this country. 

 It resembles D. lacteum, of northern Europe, from which it dif- 

 fers by having three pairs of eyes instead of one. From New 

 Jersey. 



Dendroccelum superbum Girard. Of this species I know two 

 varieties : the one is red, or rather delicate rose, the other milky 

 white. They are of a much smaller size than the preceding, 

 and are very common in rivulets, ponds, and pools of our vicin- 

 ity. It reminds us of PI. vitta, Duges, which must be placed 

 in the same genus. 



Thus, the genus Dendroccelum, of (Ersted, created by that 

 naturalist for the Planaria lactea, of MiJller, would embrace 

 three species more, the PI. vitia, of Duges, and the two above 

 mentioned. 



1 would propose a new genus for one species of this country, 

 which bears some striking resemblances to the Planaria gono- 

 cephala^ of Duges, which I would take for the type, and call 

 the genus. 



DuGEsiA Girard. The anatomical character I am not yet 

 prepared to give. As for the external appearance, the body is 

 slender, elongated, tapering away posteriorly. The head, some- 

 what detached from it, is triangular, the summit of the triangle 

 in front. 



DuGEsiA GONOCEPHALOiDES Girard. Has been found in Mas- 

 sachusetts and New Jersey, and will probably be found over a 

 greater extent. It is quite common in ponds and rivulets, and 

 differs from Duges's PI. gonocephala by the oblong shape of the 

 transparent space which surrounds the eyes, whilst in PI. gono- 

 cephala that space is circular. There are also two pairs of eyes 

 in the American species. 



He concluded with a general description of the organiza- 

 tion of these animals as illustrated by M. de Quatrefages. 



