NOS. I AND 2.] 



COTYLASPIS IN SIGN IS. 



II 



tauqua specimens the acetabnla number 29 in all, 9 in the median 

 series, 18 matching them in the peripheral series and the two 

 median peripheral ones. In my former paper I called attention to 

 the fact that Poirier's African species differed decidedly from this 

 scheme, there being in the African form 7 in the median series, 

 8 in the corresponding peripheral roAVS on each side, or 16 in all, 

 and then finally 2 median ones in the peripheral series ; in all 25, 

 as against 29 in the American form. In the 

 case of Cotylogastcr Xickerson has found that. 

 while in Monticelli's species the lateral and 

 median series correspond, in C. occidentalis 

 these two series do not correspond. 



The sucker shown in Fig. 4 of this article 

 is not, however, the invariable form at Chau- 

 tauqua. It is very general, but in addition to 

 it I have found a number of variations, as 

 indicated in the accompanying text figure. 

 These deviations have never been found to 

 occur in the anterior part of the sucker. They 

 are shown in b, c, d, e, and /", a being a copy 

 of the hind end of Fig. 4 of the plate. I have 

 found the form a, which we may call the 

 characteristic form, in 58 instances, besides 

 having met it in many more non-recorded in- 

 stances, and I have found the rest as follows : 

 h, three cases ; c, three cases ; d, one case ; e, 

 one case ; /, one case ; in all there are nine 

 cases that show variation. The variation may 

 be in having only eight instead of nine aceta- 

 bula in the median row ; this fills the gap between this and the 

 African species in that particular, or it may be in the peripheral 

 series, where we may have an acetabulum doubled, as in h, c, f, 

 or it may be the opposite that has occurred, and we find that an 

 acetabulum has failed entirely to appear as in d. These variations 

 bring the American and African forms nearer together, and unless 

 we are assured that Poirier has not overlooked a posterior median 

 acetabulum — an easy thing to do, since the walls of these aceta- 

 bula tend to cohere and the last acetabulum is verv small — we 



Diagram to show vari- 

 ation in the acetabula of 

 ventral sucker. a is a 

 copy of the posterior end 

 of PI. I, Fig. 4. b,c,d,e 

 and f are corresponding 

 views. The numbers 7 

 and 8 occupy correspond- 

 ing acetabula in each 

 diagram. 



