Our Fresh-Water Planarice. 457 



(3.) Mesostoma. Body somewhat flattered when at rest; 

 the mouth ventral, sub-central, encircled with a broad annular 

 sphincter; eyes two approximate, on the dorsum behind the 

 apex and anterior to the mouth. Lacustrine. The ova capsu- 

 lated. Dr. Johnston describes one species only, viz., If. 

 rostratum. It is elongate, elliptical, acuminate, and alike at 

 both ends, whitish and pellucid, or tinted a yellowish-red; 

 eyes reddish or black, approximate ; mouth central ; egg' cap- 

 sules dark brown or reddish, length three lines, breadth half a 

 line. This little animal I find quite common within the stems 

 of Sparganium, but owing to its small size and pellucid appear- 

 ance very easily overlooked. The reddish colour, of which Dr. 

 Johnston speaks, is owing to a number of red capsulated ova 

 often seen within the body of the animal ; I have occasionally 

 counted as many as twenty-five or thirty. The proboscis, or 

 oesophagus, is bulbous in form, with five or six strong radiating 

 muscles (see Fig. 6). It glides along the surface of submerged 

 bodies and moves rapidly in the water, which appears to have 

 suggested the epithet Velox to Dr. Johnston. I believe the 

 animal dies immediately after laying its eggs. Another species 

 (Fig. 10), the M.personatum of Dr. Oscar Schmidt, I have found 

 in a reedy pond, near Preston on the Wild Moors, Salop. I 

 have recently added it to the British fauna. See Ann. and 

 Mag. Nat. Hist, for last December. 



(4.) Opistomum. Body flattish, with an anterior sub-terminal 

 mouth ; the oesophagus pitcher shaped, not protrusile ; eyes, 

 none. Lacustrine. One British species only has been 

 described, viz., 0. serpentina, which is tongue-shaped, dilated 

 and rounded in front, lanceolate behind, white or grey, two 

 lines in length, and an inhabitant of fresh-water pools. Sir J. 

 Dalyell found this little animal, and on his authority, it is added 

 to the British fauna. It appears, from the description, to be 

 identical with the Opistomum pallidum of Schimdt. It is 

 unknown to me. 



(5.) Typliloplana. Body oblong, somewhat roundish; head 

 continous with body ; mouth sub-central, a little posterior to 

 the middle of the body ; eyes, none. Lacustrine. Two British 

 species are enumerated in Dr. Johnston's catalogue, T. foecunda 

 and T. prasina. The first is nearly linear, or a little swollen at 

 the middle, with obtusely rounded extremities, white, and half 

 a line in length; it is found in ponds in autumn. The second is 

 grass-green in colour, obtuse in front, tapering to a point 

 behind; it is gregarious, and is found in ponds in autumn. 

 Both are minute species, about half a line in length. I am not 

 acquainted with either of these species. The species belonging 

 to the genus Gonvoluta, being marine, do not come within the 

 scope of our inquiries. 



