Mr. H. J. Carter on Ploesconia and Kcrona. 247 



small as this, they have the appearance of having come more or 

 less direct from ovules or embryonic cells, which, again, is opposed 

 to the view of their being a metamorphosis of an Oxytricha or 

 Kerona, a point to which we shall have occasion to recur again 

 by-and-by. 



There is another species very like P. Charon, which is common 

 in the main drain of Bombay, and also appears to be equally 

 common in Europe, if I am right in identifying it with P. lon- 

 giremis, Duj.; but the latter is so imperfectly figured by 

 Dujardiu, that all that I can state, beyond its resemblance to 

 his delineation, is that it differs from P. Charon in the straight- 

 ness of the margin on the right side, in having no ridges on the 

 dorsal surface, in the posterior end of the " gill " being curved 

 forwards, and in having five small legs, instead of four, posteriorly 

 and laterally, viz. two on the left, and three on the right side of 

 the median line. Here, then, the short submargiual legs form 

 a valuable specific character; for the ridges on the back of 

 P. Charon are not always distinct, while the presence of longi- 

 tudinal lines on the posterior half of the ventral surface, similar 

 to those of P. truncata, may be easily mistaken for them, and 

 thus the two species, but for the short legs, confounded. 



1 am not quite certain, either, of the exact number of anterior 

 legs on P. Charon ; for in some of my sketches there are nine, 

 and in others ten. Dr. Lachmann figures ten*. 



Multiplication in P. Charon and P. longiremis by longitudinal 

 and transverse division is equally common ; and the former is very 

 likely to be mistaken for copulation, from the inferiority in size 

 of the left individual, which is frequently so small as to make it 

 appear as if they were originally derived from different sources. 



Kerona, Duj. 



Kerona pustulata, Miill. Stijlonychia pustulaia, Ehr. 

 PL VI. figs. 5-7. 



Oval elongate, soft in consistence, more or less flat ; about twice 

 as long as broad. Presenting a dorsal and ventral surface ; 

 the former more or less convex, smooth ; the latter plane, 

 irregular, and supporting a gill and legs as in Plcesconia. 

 Posterior legs five in number, fixed to the ventral surface a 

 little in front of the posterior margin, stiff, straight, styliform, 

 not used in progression ; anterior legs styliform, seven (?) 

 in number, freely moveable upon short round articulations, 

 used in progression. Oral orifice situated about the middle 

 of the body, just in front of the posterior termination of 

 the gill. Anal orifice marginal, on the left side, about the 

 * Loc. cit. pi. 9. fig. 10. 



