686 PROF. G. B. HOWES ON THE PECTORAL [DeC. 2, 



character ; they also show the basal pterygia to have arisen inde- 

 pendently (cf. ante, p. 680) by the fusion of parallel rays. This 

 being so, the fin of the Rhinobatidce, wliile clearly specialized as 

 regards the first proposition, is less modified than that of all other 

 Batoid fishes in respect to its feeble expansion. 



Until we know more than at present concerning the manner of 

 multiplication of fin-rays with bodily elongation and growth, we 

 must regard the presence of free rays in the position of those inter- 

 calated between the meso- and meta-pterygia of these fishes as none 

 other than a primitive character ; and, in respect to this, the Rhino- 

 batidce would appear to exhibit a more lowly structural feature than 

 the, for the most part, less modified Selachoidei. Whether they 

 may not have reverted to it, it is at present impossible to say ; but 

 I regard the matter as the more interesting in that Edinger has 

 attempted to show^ the prosencephalon of the Skates to be more 

 lowly than that of the Sharks, and that I have found" the primitively 

 continuous dorsal mesentery of the alimentary viscera to be alone 

 retained by the Torpedo Hypnos subnigrum among living Plagio- 

 stomes. It raises, among other things, the question whether this 

 type of fin-skeleton, which Huxley^ would apparently associate with 

 his "multibasal" one, may not represent the (admittedly modified) 

 survivor of a type more primitive than that of the living Selachoidei, 

 rather than a culminating term in a series of changes which he has 

 pictured {I. c. p. 52) as of the nature of an expansion with interpo- 

 lation of postaxial rays, under a shortening up of the supposed 

 " archipterygium." 



For the greater part of the material upon which this investigation 

 is based, I stand indebted to the late Dr. F. Day, and, through my 

 honoured master Prof. Huxley, to Mr. Ramsay (of the Sydney 

 Museum), to whom we owe the possession of the Australian forms. 

 My thanks are also due to my friend Mr. G. A. Boulenger for a 

 continuance of that assistance and advice extended to me on former 

 occasions, and to my friend and former pupil Dr. J. Beard for the 

 reference to Edinger's work cited. 



P.S. — Since this paper was written Mr. Boulenger has directed my 

 attention to a short paper recently published by O. Jaekel*, in which 

 the author arrives at the conclusion that the Batoidei are of poly- 

 phyletic origin. He bases this upon the study of the disposition of 

 the gill-slits, of the translocation of the pectoral fin in relation 

 thereto, among living forms, and of certain facts of palaeontology. 

 I am, on the whole, disposed to accept the spirit of his conclusions ; 

 but my own researches suggest that, setting aside the Ceratopterina 

 (which may possibly be related to the Rhinidce) and Pristis (which 



^ Abhandl. d. Senckenbergsche Gesellsch. nat. Frankfurt, Bd. xv. 1888, p. 102 



=" This vol.. p. G71. 



^ P. Z. S. 1876, cf. pp. 52, 58, 59. 



* Sitzuugsb. d. Gesellsch. naturf. Freunde, Jhrg. 1890 (no. 3), p. 47. 



