. Carnegie Institution of Washington publication. 144 CHIM.^ROID FISHEvS AND THKIR DEVFXOPMENT. was provided with a well-marked dorsal fin which was supported anteriorly by a spine. This fin, it may be remarked, is the earliest dorsal known in Chimaeroids, and its structure, therefore, deserves more than passing mention. Thus, as shown in fig. 140, and in the series of figures, figs. 143 a, b, c, d, its position is further hindward than in recent forms, in this regard suggesting interestingly the condition of shark. It is also noteworthy that the base of the myriacanthid spine is not articulat
. Carnegie Institution of Washington publication. 144 CHIM.^ROID FISHEvS AND THKIR DEVFXOPMENT. was provided with a well-marked dorsal fin which was supported anteriorly by a spine. This fin, it may be remarked, is the earliest dorsal known in Chimaeroids, and its structure, therefore, deserves more than passing mention. Thus, as shown in fig. 140, and in the series of figures, figs. 143 a, b, c, d, its position is further hindward than in recent forms, in this regard suggesting interestingly the condition of shark. It is also noteworthy that the base of the myriacanthid spine is not articulated to the fused mass of anterior epichordalia, but is still connected with a hinder independent plate, b, which, we suggest, becomes in recent Chimjeroids the articular process of the anterior cartilaginous plate. A further correspondence with a shark-like condition is noticed in the separation of the fin basis into proximal ("basal") and distal ("radial") moieties; in recent Chimaeroids these are repre- sented by but a single plate, c. It should be finally observed that the vertebral column of Myriacanthus, fig. 143 B, shows anteriorly a segmentation which reasonably indicates the presence of Fig. 140.—Head region o( the Jurassic Chim^roid Myriacanthus. After Egerton s specimen, in British Museum. C. Centra; 5. Detached ventro-median chisel-shaped "; Summarizing our knowledge of Mvriacanthus, we note that its dermal defenses are far more highly specialized than in Squaloraja, and that it has evolved an addi- tional pair of tritoral plates in the upper jaw, as well as a ventro-median element in the mandible. Furthermore, that its frontal clasping organ, although still spine- shaped, is less like a spine than in Squaloraja [cf. figs. 131, 132, and 133). On the other hand, in its dorsal fin and in its fairly evident vertebrae it is more distinctly shark-like than any other Please note that these images are extracted from
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