630 MR. A. SMITH WOODWARD ON SOME [NoV. 18, 



1844. Aspidorhynchus comptoni, L. Agassiz, Comptes Rendus, 

 vol. xviii. p. 1009. 



The horizon from which the Brazilian fossils were obtained has 

 long been well known. The fish-fauna was briefly noticed by 

 Agassiz so long ago as 1841 and 1844 (loc. cz7.), and Prof. Cope 

 described one of the genera in 1871 \ while the present writer treated 

 another genus at still greater length in the 'Proceedings' of this 

 Society, June 23rd, 1887 ^ As in the case of Rhacolepis, already 

 described, the examples of Belonostomus occur in nodules in a beauti- 

 ful state of preservation, though, on account of the form of the 

 fish, the specimens are always incomplete. As a rule, the long body 

 is bent upon itself at about the middle point, the tail thus lying in 

 close proximity to the head (Plate LTV.) ; and in no instance is the 

 slender elongated snout completely preserved. Several typical por- 

 tions of the fish are shown in the accompanying drawings (Plates LIV., 

 LV.), and the Brit. Mus. register-numbers of some of the more im- 

 portant specimens are placed in brackets after the various descriptions 

 of anatomical characters which they specially demonstrate. All 

 measurements are given in decimal fractions of the metre. 



General Form. — Owing to the death-contortion, it is not readily 

 possible to estimate the precise proportions of the fish under consi- 

 deration. The trunk, however, must have sometimes attained a total 

 length of not less than 0-55 ; and the maximum depth of such an 

 individual, shortly behind the pectoral arch, would be about 0'08. 

 The total length of the head and opercular apparatus of a fish of this 

 size would probably not exceed 0*24. As usual in the genus, the 

 head and trunk are much laterally compressed, and the fins are 

 relatively small. 



Head and Opercular Apparatus.— The long, narrow cranial roof is 

 flattened in the middle and beautifully ornamented with close, thick, 

 vermiculating rugse of ganoine, which have numerous short branches, 

 and are chiefly disposed in a longitudinal direction upon the rostral 

 region (no. 15495 a). Behind the parietals, a pair of large supra- 

 temporal plates continues the roof backwards as far as the hinder 

 extremity of the upper border of the operculum (no. P. 975 i). In 

 advance of the frontals, the snout tapers rapidly into a very slender 

 rostrum, of which the base is shown from above in Plate LV. fig. 1. 

 Seen in profile (no. P. 3810), the much elongated frontal and ros- 

 tral region inclines gradually downwards from the short parietal 

 region, which continues the dorsal plane of the trunk ; and the nar- 

 row, well-developed parasphenoid bone is parallel with the parietal 

 roof. There are extensive ossifications in the otic region, but no 

 interorbital septum occurs. A remarkable pair of large longitudinal 

 tubular ossifications is also shown in transverse sections of the rostrum 

 (Plate LV. fig. 2), these structures extending almost or quite as far 

 backwards as the orbital space. They are probably ethmoidal in 

 character, and destined for the protection of the elongate pedicles 

 of the olfactory lobes. The bones of the mandibular, suspensorium 



^ A7iadopoffon, E. D. Cope, Proc. Amer. Phil. Soc. vol. sii. (1871), p. 53. 

 (Founded upon the uudescribed Cladocyclus qardncri, Agass.) 



2 Ehacokpis, Smith Woodward, P. Z. S. 1887, pp. 535-542, pis. xlvi., xhii. 



