. Chimæroid fishes and their development. Fishes; Chimaeridae. JURASSIC CHIM^ROIDS. 143 The second Jurassic Chimaeroid, Myriacanthus, is known, unfortunatel\', in less detail. Nothing has been definitely ascertained regarding its general shape or the structures of its trunk. But what is known of its head region shows that it possessed extraordinary features. The form of the head was, in general, like that of Callorhynchus, terminating in a long snout. This had a somewhat foliaceous tip (fig. 140), as in the recent genus, but, on the other hand, was broader, less acutely pointed, and studded do
. Chimæroid fishes and their development. Fishes; Chimaeridae. JURASSIC CHIM^ROIDS. 143 The second Jurassic Chimaeroid, Myriacanthus, is known, unfortunatel\', in less detail. Nothing has been definitely ascertained regarding its general shape or the structures of its trunk. But what is known of its head region shows that it possessed extraordinary features. The form of the head was, in general, like that of Callorhynchus, terminating in a long snout. This had a somewhat foliaceous tip (fig. 140), as in the recent genus, but, on the other hand, was broader, less acutely pointed, and studded dorsally with shagreen denticles and dermal plates. The best example of a snout of M3rriacanthus belongs probably to a specimen in the Jermyn Street collection, of which a sketch is given in figure 141. The figure, which shows the snout in dorsal aspect, indicates also the spine-like nature of the frontal clasping organ. This organ is shown again, in lateral view in fig. 133. There can be little question that in this genus the shagreen-like defenses seen in the head of Squaloraja are replaced by a number of conspicuous pairs of dermal plates, some of which attain a large size and are furnished with spinous outgrowths. Thus, for example, on either side of the jaw (slightly schem- atized in fig. 142) there is a conspic- uous "trachyacanthid " spine bearing a large serrate row of four or five subspines. These elements, it may be remarked, are well shown in a second specimen from L3'me Regis, in the Jermyn Street collection, and in Egerton's type specimen of Prog- nathodus gucnthcri (yMyriacantlius par- adoxus), now preserved in the British Museum, in which one of these spines is shown in sihi, attached to the broad jaw. The arrangement of the dental plates of Myriacanthus is known with fair accuracy (fig. 119). The mandibular plates show foldings on the visceral face and in these folded areas appears the most conspicuous aggregation of tritoral points. A somewhat similar
Size: 1637px × 1526px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectfishes, bookyear1906
