4 PROF. G. B. HOWES ON THE SKELETON AND [Jan. 18, 



there came under my notice a short paper by Traquair (26, p. 143), 

 in which he describes the restoration of parts of the tail of Proto- 

 pterus. Finding that he had discovered certain irregularities in the 

 skeletal elements of the said restored tails, and knowing that Haswell 

 had recorded (15) some irregularities of the Ceratodus paired fins, 

 it occurred to me that the same determining cause might have been 

 at work in the two cases — i.e., that Haswell's "branching" fins 

 might perchance be " restored " ones, like Traquair's. I was soon 

 undeceived ; for, apart from Haswell's paper, I have had the good 

 fortune to examine one such fin, sent by him to Prof. Huxley. The 

 deductions arrived at in the sequel have arisen out of a study of 

 it and of the fins of five other individuals. Three of them were 

 kindly lent me by my master, Prof. Huxley ; of the two which 

 remain, one forms part of our teaching-collection at South Ken- 

 sington ; for the loan of the other I am indebted to my Demon- . 

 strator, Mr. M. F. Woodward. 



It is remarkable that Giinther, in his Monograph on Ceratodus 

 (14), does not mention Traquair's discovery already alluded to. It 

 is clear that that author's paper must have escaped him, as I fail to 

 find note of it under either " Pisces " or " Ganoidei," as reported by 

 him for the ' Zoological Record ' during both its year of publication 

 and the succeeding one. 



The structural plan of the fin of Ceratodus is too familiar to merit 

 detailed description here, Huxley has described (19, p. 46 e? seg.) 

 its general features with exceeding care, and I shall, in accordance 

 with his system, speak of the segments of the axis as " mesomeres." 



The lateral rays will be described, under the same nomenclature, 

 as paratneres ; those which look dorsally when the fin is j)laced 

 against the side wall of the body (anteriorly when it is held out at 

 right angles thereto) I shall speak of as preaj:ial ; those which 

 look ventrally under the first-named condition (posteriorly under the 

 last-named) I shall describe as posiaxial. Preaxial and postaxial 

 correspond to the " dorsal " and "ventral" of the Germans. As 

 the basal segment of the axis differs in its essential characters from 

 those which follow upon it, I shall refer to it as the proximal meso- 

 mere (the " zwischen-Stuck " of Davidoff (7), the " erste Glied" of 

 Schneider (23)). 



II. On the Structure of the Ceratodus Paired Fins in general 

 and of the Pelvic Fins in particular. 

 The majority of observations made thus far upon the fins of 

 Ceratodus bear especially upon the pectoral member ; its pelvic 

 representative has received less attention. DavidofF (7) and Haswell 

 (15) have dealt most fully with it, the last-named author espe- 

 cially as to certain "irregularities" mentioned in the Introduction. 

 Fig. 1 is a faithful representation of the pelvic fin presented by 

 him to Prof. Huxley ; and as it does not appear to correspond 

 with any one figured in his own paper, I proceed to describe it in 

 detail. 



The fin reached me cleaned and prepared, as represented in the 



