22 THE EOTIFEEA. 



tary canal was large, not visibly separated, and filled with food of a rich dark-brown 

 hue. The toes are long, slender, acute, and slightly decurved. The auricles, which 

 were freely protruded, are rather small. P.H.G.] 



Length, -^ inch. Habitat. Sandhurst, Berks ; Epping Forest ; Woolston, Hants 

 (P.H.G.) ; pools : rare. 



N. CYRTOPUS, Gosse, sp. nov. 

 (PI. XVII. fig. 7.) 



[SP. CH. In form resembling N. aurita, but very much smaller, and mor& slender 

 in proportion ; brain intensely opaque ; no visible auricles ; toes long, decurved. 



This little species I had known from a single specimen just dead, in August 1851, 

 which I found in water from Widcombe Pond, Bath. I had never met with it again 

 till June 1885, when I found a second in water from Woolston, and subsequently many, 

 from many localities. It much resembles N. aurita ; but is smaller ; and the toes are 

 slender and decurved. A pair of colourless specks, like air-globules, are in its front, 

 which may be eyes, and a large brain, which carries at its hinder end an aggregation of 

 opaque matter forming a collection of round cells. This, by refracted light, is intensely 

 black, as in aurita, and renders the species very conspicuous, reaching far down into the 

 body-cavity. The mastax is normal ; the alimentary canal also large, not visibly 

 divided ; ovary and contractile vesicle as ordinary. 



In manners it is particularly sluggish, scarcely changing its place, though in con- 

 stant motion. It roots and nibbles among the floccose sediment, and affects conceal- 

 ment, seeking the shelter of the thin integument of decaying Nitella, and such-like 

 plants, under which it hides ; and, if it creep out for an instant, presently betaking 

 itself to its refuge again, where it twists and turns restlessly on its centre. P.H.G.] 



Length. About T ^ inch. Habitat. Bath ; Woolston ; Sandhurst, Berks ; Epping 

 Forest; Cheltenham (P.H.G.) ; pools: not common. 



N. TKIPUS, Ehrenberg (nee Ley dig.) 

 (PI. XVII. fig. 4.) 



[SP. CH. Body thick, arched dorsally, diminished behind to a conspicuous tail, 

 and furcate toes ; tail equal in length to the toes ; brain opaque ; auricles small, 

 slender. 



I know this animal by a single specimen, which I found among Myriophyllum in a 

 tank in my own garden, near London, in 1854. It has never occurred to me again ; 

 and I do not feel quite certain that it is the tripus of Ehrenberg. The body is marked 

 by several strong folds of the skin. Viewed from the side it is arched, and the ventral 

 outline is concave ; but the ovary was undeveloped, which fact might modify the form. 

 The frontal cilia are set on a large ovate area looking ventrally (fig. 4), so that 

 ordinarily the front appears rounded and free from cilia. Occasionally, however, the 

 front is elevated and expanded somewhat angularly, and an auricle is thrust out on 

 each side, of somewhat serpentine outline, set on its anterior edge with vibratile cilia, 

 whose effect is manifest in accelerated motion. The brain runs down to a long obtuse 

 point in the occiput, whose extremity, in my example, was occupied (fig. 4a) with some 

 irregular granules of opaque matter ; seated on the end of which was a large pear- 

 shaped red eye. The posterior extremity of the trunk runs out into a prominent tail, a 

 tapering cone, with alternate constrictions and swellings. Beneath this are the furcate 

 toes ; and as the tail is of the same length as these, and diverges at a like angle, forming 

 three angles of a triangle, the animal well deserves its specific name. P.H.G.] 



Length, T ^ inch. Habitat. A garden pan, near London (P.H.G.). 



