Vol.62.] OF MYBIACANTHUS PARADOXUS, 3 



The frontal spine or tenaculum (t) is only partly shown in left 

 side-view ; but it was obviously expanded at the base, and tapered to 

 a point distally. It is relatively small, and its size denotes that the 

 animal to which it belonged was immature. 1 The teeth and fin- 

 spine, indeed, are only about two -thirds as large as those in the 

 larger and best-known examples of the same species. Scattered 

 beneath the anterior half of the tenaculum and farther forwards 

 on the rostrum are numerous small hooklets, which doubtless 

 originally assisted in the prehensile functions of the spine. Each 

 of these hooklets (PL I, fig. 3) is a polished recurved point fixed on 

 an expanded base, which is marked by radiating furrows. Very 

 minute hooklets and stellate tubercles of similar shape (fig. 3 a) are 

 also visible in a patch on the anterior part of the fossil, and perhaps 

 at the base of the dorsal fin-spine. They have already been noticed 

 in the skin of the allied genus Ghimceropsis from the Bavarian Litho- 

 graphic Stone. 2 It is curious that there are no traces of calcified 

 rings marking the course of sensory canals. 



In addition to the frontal spine and hooklets just described, 

 there are also remains of two, or perhaps three, pairs of the tuber- 

 eulated dermal plates, which have already been noticed in other 

 specimens. The most anterior pair preserved (i) is that of which 

 one plate is well shown in the type-specimen of Prognathodus 

 Guentheri described by Egerton. The hollow, ridged plate (fig. 4) 

 is ornamented by rows of smooth tubercles which radiate down 

 the sides from the summit ; and its ridge is surmounted by large, 

 longitudinally striated spikes, of which only two are exhibited in 

 the new fossil, but of which there are four in a specimen in the 

 Museum of Practical Geology (fig. 5). 3 One of a pair of narrow 

 ridged plates is exposed from its attached face farther back in the 

 fossil (in) ; and this is evidently identical with a plate represented 

 in another specimen in the British Museum. 4 At the base of the 

 tenaculum there is part of another plate (ii), which may be the 

 fellow of that just mentioned, or may belong to an intermediate pair. 



The straight dorsal fin- spine, exposed in left side-view (d.f), is 

 much crushed, and has accidentally lost nearly all its thorn-shaped 

 denticles ; but it is interesting, as displaying for the first time the 

 complete base of insertion. This base is comparatively short, and 

 tapers to a bluntly-pointed lower extremity. The very slender apical 

 part of the spine is almost destitute of tubercles on the sides, but is 

 marked with conspicuous longitudinal striations. 



The new fossil thus warrants the conclusion that Myriacantliv.s 

 is a Chimseroid closely similar to the Upper Jurassic Chimceropsis, 

 with (i) a median chisel-shaped tooth in front of the lower jaw ; 

 (ii) a few tuberculated dermal plates on the head ; and (iii) a tuber- 



1 On the growth of the frontal spine in male Chimaeroids, see A. Giinther, 

 'Report on the Deep-Sea Fishes,' Challenger Keports, vol. xxii (1887) p. 12. 



2 K. A. von Zittel, « Handbuch der Pataontologie ' vol. iii (1887) p. 113. 



3 B. Dean, ' American Geologist' vol. xxxiv (1904) p. 52 & pi. ii, fig. C. 



4 'Catalogue of Fossil Fishes' pt. ii (1891) pi. ii, fig. 2. 



u2 



