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Show 1890.] FIN-SKELETON OF BATOID FISHES. 683 middle (axis), and this, which occupies the position of Gegenbaur's intercalary ray (I. c. pl.ix. fig. 14), appears to me to indicate the apposition point of parts representative of the meso-andneo-pterygiaof the Trygonidce and Raiidce. Viewed from this standpoint, the pectoral fin of Myliobatis is in complete structural harmony with that of the Trygonidce, 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 metapterygium in a varying degree. It is interesting here to recall m y belief in the fusion of the meso- and neo-pterygia of Trygon, and to remark that the specimens of Tr. uarnak 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 the Torpedoes 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 LLypnos. 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 Myliobatis (cf. figs. 1, 3, and 10). The mesopterygium of the Torpedinida 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 mesopterygium of the Raiidce and of the Selachoidei, hypertrophied and vertically enlarged to form a stay for the massive propterygium. There can be no question that rays answering to the intercalary series of the Raiidce, Trygonidce, and Myliobatis (with their products) 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. 11) 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 ( f 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- |