Mr. H. J. Carter on PlcEsconia and Kerona. 243 



me, and that too without acknowledging- the sources from which 

 they have been derived. 



With these preparatory remarks, then, let us proceed with the 

 PlcesconicE first, as they are the highest in the scale of develop- 

 ment. 



Plcesconia, Duj. 



Plcesconia truncata. Euplotes truncata, Ehr. PI. VI. figs. 1-4. 



Oblong, oval, shield-like, firm in consistence, more or less dis- 

 coidal according to the distension of the abdominal cavity ; 

 about twice as long as broad. Presenting an upper or dorsal 

 and an under or ventral surface. Dorsal surface convex, 

 smooth. Ventral surface plane, irregular, furnished with large 

 and small legs, and a kind of gill. Gill situated on the left 

 side anteriorly, and consisting of a ladder-like row of bars or 

 narrow sessile plates, which, commencing on the left margin 

 in front, extends backwards and inwards obliquely, to termi- 

 nate in a more or less attenuated form just behind the middle 

 of the body ; larger legs scattered over the right two-thirds of 

 the ventral surface, which is defined by a wavy longitudinal 

 line on the left side, forming, with the obliqvie border of the 

 gill, a triangular area open in front, which terminates behind 

 in a pointed depression leading to the oral orifice. Oral 

 orifice situated a little behind and to the left side of the 

 middle of the body, just in front of the termination of the gill. 

 Large legs thirteen in number, supported on short articula- 

 tions, and divided into an anterior and posterior set ; posterior 

 set largest, five in number, of which the three on the right 

 side are fixed to the ventral surface about the junction of the 

 middle with its posterior third, and the two others a little 

 further back, all extending a short distance beyond the pos- 

 terior margin of the body, and each cleft at its termination 

 into a lash of hairs, successively longer than each other, and 

 capable of being closed or expanded at the will of the ani- 

 malcule; anterior set eight in number, styliform, not cleft, 

 fixed chiefly to the anterior part of the ventral surface, where 

 the two on the left side in front are the largest. Short legs 

 four in number, situated posteriorly and laterally, two on the 

 right and two on the left side, fixed to the ventral surface 

 submarginally ; those on the right side terminating in an ex- 

 panded lash of hairs respectively, and the two others styliform. 

 Posterior and lateral margins of the body sharp, smooth, even, 

 defined; anterior margin divided into two lips, forming a 

 groove which is closed on the right and open on the left side, 

 in which a wreath of long curved cilia are fixed, that dimi- 

 nish in length towards the left side, and terminate at the 



16* 



