4 Prof. H. James-Clark on the Affinities of 



centrum is stated to be at the anterior edge of the ventral face : 

 " Fig. 1 von der Seite gesehen, Bauchflache rechts mit dem 

 Munde am vorderen llande." In Peridinium Cypripedium this 

 aperture is on the ventral side and about halfway between the 

 two ends of the body — a position which it seems to occupy in 

 many of the Peridinisea. 



Although I do not use the word spiral in regard to the mouth 

 and oesophagus, it can hardly be said that I "mention nothing 

 spiral " about them ; for I think that the illustrations tell as 

 much as the text ; and any one who will inspect my figures 2 & 3 

 will see that the position of the mouth in the first, and the trend 

 and curve of the oesophagus in the second, are sufficiently indi- 

 cative of a spiral arrangement of these parts. The text fully 

 bears out this assertion, in the following words (p. 397; Annals, 

 p. 274) : — " The mouth lies altogether within the posterior 

 obliquely transverse furrow {pf), and extends from its anterior 

 to its posterior edge, trending diagonally across the axial plane 

 of the body, from the right, backwards, towards the left ;" and 

 on p. 398 (Annals p. 275), " From the mouth the oesophagus {ce) 

 passes obliquely backwards and towards the dorsal region, at 

 least halfway through the body, and then terminates rather 

 abruptly just before the contractile vesicle, but a little to the 

 right side (fig. 3 oe) of the axial plane." Lest, however, there 

 should be any further doubt in regard to my views upon this 

 point, I will state now that the arrangement of the mouth and 

 oesophagus is decidedly spiral, and unequivocally stamps this 

 animal as a member of the Iseotropic division of Infusoria 

 Ciliata. 



As to the systematic position of this Peridinium, its Inotropic 

 character at once removes it out of the division to which the 

 Vorticellina belong ; but yet when we see that one of the latter 

 family, viz. Trichodina Pediculus, Ehr., has its contractile vesicle 

 on the left side of the body, instead of on the right — thus par- 

 tially reversing the relationship of the organs as exhibited in 

 the other members of that group (see my paper in the Mem. 

 Boston Soc. Nat. Hist. vol. i. 1866), and that it totally lacks 

 the protrusiie vibratory disk, so eminently characteristic of the 

 Vorticeliidse — and when, again, we call to mind the ciliated body 

 of another Vorticellidan, viz. Claparede's Jrichodinopsis, the 

 way appears clear for the close approximation to the Vorticellina 

 of the totally ciliated Tintinnoidea with their terminal, depressed, 

 cyathiform front, bordered by the crown of cilia, which termi- 

 nates, according to Claparede, by passing into the excentric 

 mouth: and then, as a succeeding step, it does not seem at all 

 improbable that the Peridinisea, judging from the characters of 

 P. Cypripedium, should have a not very remote affiliation with 



