6 On Peridinium Cyprlpedium and Urocentrum Turbo. 



figures it as having an ovate three-cornered body, " corpore ovato 

 triquetro/' and states that the stylus or tail equals one-third the 

 length of the body, " stilo tertiam corporis partem sequante ;" 

 whereas the American Peridinium has an " oblique pyriform 

 outline," and the so-called flagellum is at least half as long as 

 the body. 



Between the statements of Ehrenberg and Claparede there is 

 such a marked discrepancy that I am pretty well convinced that 

 the testimony of the latter cannot by any means be used as an 

 adjunct to the description of the former; for whilst Ehrenberg 

 speaks of the "corpore non ciliato, fronte ciliis coronata," 

 Claparede states (p. 7^), in the first place, that there are no 

 other organs than the buccal cirri, but that (p. 135) "it is the 

 inferior part of the [transverse median'^ furrow that carries the 

 buccal cirri ;" and secondly, that " the mouth is not placed where 

 Ehrenberg figures it \i. e. at the anterior edge of the ventral 

 plane], but is lodged in the transverse median furrow which 

 that author represents." 



Supposing, now, the animal of Ehrenberg to be the same as 

 that of Claparede, and the one described by me likewise identical 

 with the former, then we must believe that Claparede has com- 

 mitted a great oversight in not seeing the most prominent and 

 conspicuous cilia, in the region of the anterior annular furrow, 

 as described by me, and which, in this assumed case, are in a 

 corresponding position with the vibrating cilia-crown about the 

 anterior, flat, frontal plane ("um die vordere fiache Stirnfiache 

 einem wirbelnden Wimperkranz ") which Ehrenberg describes. 

 It hardly seems possible that Claparede should have detected 

 the smaller cilia in the median transverse furrow and overlooked 

 the larger and more conspicuous ones, whilst Ehrenberg, with 

 his far less powerful lenses, appeared to find no difiiculty in 

 making out the latter. It seems therefore much more plausible 

 that the Urocentrum of Ehrenberg is not the same as that of 

 Claparede, and certainly more likely that the latter should have 

 failed to appreciate the value of the observations of the former 

 upon the anterior cilia-crown than that he should have over- 

 looked it were it really present. 



I scarcely need add, therefore, that I am at least equally con- 

 fident, if not fully satisfied, that Peridinium Cypripedium is not 

 the same as the Urocentrum of Claparede. 



Cambridge, Mass., May 12, 1866. 



