1890.] FIN-SKELETON OF BATOID FISHES. 687 



has gone already), those BatoiJs which remain would fall into two 

 great series — one including the Rhinobatidce, Raiidce, Tryjonidce, 

 and most probably the Myliobatidce, which might be provisionally 

 termed the Batoidei veri, as distinguished from the Torpedifiidce 

 or Batoidei non veri. 



Jaekel has failed to recognize one character of especial interest at 

 the present juncture, viz. the presence in many Batoids of a vestigial 

 (sixth) pair of gill-slits. These are disposed lineally with the func- 

 tional ones and immediately below (ventrad of) the coracoid cartilage. 

 Parker refers to them in Raia nasuta as "looking like an obliterated 

 sixth pair of gill-slits." I fail to see that any other interpretation 

 is possible, and their position and relationships appear to me to 

 warrant the conclusion that the pectoral girdle of the Plagiostomi 

 has, with its related fins, undergone a translocation forwards pro- 

 portionate to the shortening up of the branchial apparatus by sup- 

 pression from behind. 



VI. — The Pectoral Fin-Skeleton and Affinities of the Liassic 

 Squaloraja polyspondyla. 



My friend Mr. Smith Woodward, in his excellent paper on this 

 fish^, seeks to associate it with the Sharks and Rays (p. 537), and he 

 would create for its reception the family Sqiialoraiidce of the Setachii 

 Tectospondyli. He figures and describes the pectoral fin-skeleton 

 with perfect accuracy, and he regards the anterior of the two 

 basal cartilages which support it as (/. c. p. 536) either "the 

 coalesced pro- and mesopterygium" or "mesopterygial, with a 

 minute indistinguishable propterygium at its proximal angle." In 

 this I believe him to be mistaken. He bases his conclusions, as 

 need hardly be said, upon analogy to the living forms ; but on 

 appeal to them another, and to my mind more forcible, comparison 

 may be instituted. I have previously attempted to show" tliat the 

 paired fins of the Chimseroids are destitute of a mesopterygium, and 

 that Mivart was right in regarding the two-jointed ray of the anterior 

 border of their pectoral fin as a propterygium. Very shortly after 

 the reading of Mr. Smith Woodward's paper, I had the good fortune 

 to examine his specimens ; the conclusion that the pectoral fin of 

 his fish was that of a Chimseroid forced itself upon me at the time ; 

 and as all subsequent consideration has the more fully persuaded 

 me that this is so, I avail myself of the present opportunity of 

 recording my belief. 



It is, unfortunately, impossible to say whether the propterygium 

 of Squaloraja was or was not segmented ; its posterior border appears 

 to hare been thickened and keel-like throughout its proximal region, 

 and examination under a lens reveals the presence of an interspace 

 between the ridge in question and the base of the metapterygium. 

 The Chimferoid metapterygium. differs from that of all known 

 Sharks in its gradual increase in depth from behind forwards, and 



1 P. Z. S. 1886, pp. 527-538. ^ P. Z. S. 18S7, p. 23. 



46* 



