Our Fresh-Water Planarice. 455 



margins in elegant folds. The normal number of eyes is two, 

 but there are occasionally four, in Avhich case the anterior pair 

 is very minute. Dr. Johnston says it inhabits cold springs 

 and lakes, is gregarious, and not common. I find it in the 

 canal near my house, and in pools in the neighbourhood, 

 tolerably abundant, and have never any difficulty in procuring 

 specimens for examination. I do not consider it more 

 gregarious than other species. 



P. torva. This is a very quaint looking fellow ; its two 

 black eyes, which are of a crescent form, are partly surrounded 

 by a white ring or halo, which gives the creature a squint-like 

 look : suggesting, probably from its sinister appearance, a dis- 

 position conveyed by the epithet, "torva." It is described 

 as being cinereous or black, on the dorsal, and greyish on the 

 ventral surface. The front is obtuse, rounded on the angles, 

 and projecting in the centre. It deposits a large oval capsule, 

 and is six or seven lines long, by about two broad. 



I have recently met with some very large velvety-black 

 Planarice, which resemble P. torva, in having a white halo 

 round the eye spots; but I have reason for believing that 

 they are individually of a distinct species. The black eye- 

 specks in the surrounding uncoloured halo are not visible 

 under a simple lens in the individuals I am speaking of; 

 but the compound microscope of about twenty diameters 

 reveals them. In P. torva, the eye-specks are very apparent 

 under a simple lens : the colour is of a decided black when 

 viewed by reflected light; in size it is almost equal to the 

 large P. lactea, and it often crenulates its margins like it, 

 but only very slightly. I do not find any other Planarice like 

 the ordinary P. torva in the water whence I obtain these large 

 individuals, and I am inclined to regard them as, if not a dis- 

 tinct species, at any rate a well-marked variety. I have occa- 

 sionally found a P. torva with four eyes, each pair with the 

 characteristic white halo ; the anterior ones in this case are 

 small, as in P. lactea when possessed of four eyes. I have 

 little doubt that this four-eyed variety of P. torva is the Tetra- 

 celis fontana of Diesing ( ff Systema Helminthum," i., p. 191), 

 who thus describes it : — " Corpus depressum ellipticum, antice 

 truncatum, fuscum. Ocelli geminati nigri in macula alba, pos- 

 tici reniformes majores. Longit. &" , latit. 14/"." 



P. Arethusa is described as being truncate and auriculate 

 in front, leaden or slate grey, paler underneath, having a black 

 eye on a white spot on each side of the medial line in front. 

 Length, six lines ; breadth, one line. It is said to be common 

 in pure springs and rivulets. I do not know this species. 



P. Pclinensis inhabits pure springs, and is rare. It is the 

 smallest of the fresh-water Planarice, being only three lines 



