1890.] FIN-SKELETON OF BATOID FISHES. 683 



midcile (^axis), and this, which occupies the position of Gegenbaur's 

 intercalary ray {I. c. pl.ix. fig. 14), appears to ine to indicate the ap[)o- 

 sition point of parts representative of the meso-andneo-pterygiaof tlie 

 TrygonidcE and Raiidce. Viewed from this standpoint, the pectoral 

 fin uf Myliohatis is in complete structural harmony with that of the 

 Trygonidcs, as represented by Pteroplatea. Its propterygium is in 

 articulation with both the girdle and the mesopterygium, and the 

 whole differs chiefly from the Trygonid fin in the fusion of its 

 parts — a dominating peculiarity which extends even to its metaptery- 

 gium in a varying degree. It is interesting here to recall my belief 

 in the fusion of the meso- and neo-pterygia of Trygon, and to remark 

 that the specimens of Tr. uarnalc under my hands show signs of 

 fusion between the axial basal plate and the pro- and meta-pterygia. 

 A belief in affinity between the Trygonidce and Myliobatidce thus 

 becomes justifiable ; and, so far as the pectoral fin-skeleton goes, 

 the latter family would appear to realize a culminating term in the 

 series. 



Torpedinidce. — The basal skeleton of the pectoral fin of tlie Tor- 

 pedoes is one of the most perplexing with which I have had to deal, 

 not because of its structure but rather of its affinities, as the sequel 

 will show. It has been described by Gegenbaur for Torpedo, and 

 by Haswell for Sypnos. I have been able to examine it in both 

 genera and in Astrape ; and to the general descriptions of the authors 

 named I have nothing to add, except that neither seems to have 

 sufficiently recognized the presence of an articulation of the pro- 

 upon the meso-pterygium as in Pteroplatea and Myliohatis (cf. figs. 

 1, 3, and 10). 



The mesopterygium of the Torpedinidce is a remarkable structure. 

 Both in the number of its rays and in its general relationships, 

 as in the composition of its articular facet, it suggests the meso- 

 pterygium of the Raiidce and of the SelacJioidei, hypertrophied and 

 vertically enlarged to form a stay for the massive prapterygium. 

 There can be no question that rays answering to the intercalary 

 series of the Raiidce, Tryyonidce, and Myliohatis (with their pro- 

 ducts) do not enter into its composition ; and, in the absence of 

 these, the Torpedo's fin differs from that of all other Batoids. In 

 one specimen (fig. 10) I observed a fusion of the bases of two rays 

 next in order behind the mesopterygium ; and the resulting minute 

 plate {np. 1 1) showed signs of intercalation between the meso- and 

 meta-pterygia, suggestive of its being the vanishing vestige of a 

 neopterygium. The marked abbreviation of the metapterygium so 

 characteristic of these Torpedinidce appeared at first glance to favour 

 the suggestion, but I have been unable to find further support 

 for it; and, indeed, similar and more marked fusions had affected 

 the two posterior rays of the propterygium (;| of fig.), in common 

 with other parts of the same fin. 



There is something in the above at complete variance with that 

 seen in all other Batoids ; and, except for its rotation forwards and 

 fusion with the head, the pectoral fin of the Torpedinidce is that of 

 a Shark. Gegenbaur has insisted {I. c. p. 84) upon the marked dif- 



