636 ON SOMIC UPPER CRETACKOUS FISHES. [Nov. 18, 



similar to the typical members of the genus of late Jurassic age, that 

 they may be regarded as proving the persistence of this somewhat 

 specialieed type during a long period and over wide areas of the 

 earth's surfiice. That is a feature of some interest in the evolution of 

 the group. But if Apateopholis be correctly interpreted in the fore- 

 going description, this genus is still more noteworthy as presenting 

 probably the latest phase in the specialization of the family-type. 

 It would appear that in the Aspidorhynchidfe, as in most groups, 

 the degeneration of the squamation is a character indicating high 

 degree in development, and it is quite possible that further researches 

 may prove some intimate connection between this family and the 

 problematical Hoplopleuridse, which are so characteristic of Upper 

 Cretaceous formations, and are generally considered to include at 

 least one genus {Prionolepis or Aspidopleurus) with a single series 

 of deep flank-scales like those of Belonostomus. It is further of 

 interest to note that the development of a preopercular spine is a 

 feature hitherto unknown even in the most specialized of Phj sostomous 

 fishes ; Apateopholis, in this respect, being paralleled only by some 

 of the highest Pliysoclysti. 



With regard to the origin of the family, the typical genera, 

 Aspidorhynchus and Belonostomus, so far as knovpn, appear suddenly 

 in the Lower Oolites ' ; and no intermediate stages occur between 

 these rostrated forms and the more ordinary " ganoids" of earlier date. 

 It is, however, worthy of note that, so low in the Mesozoic Series as 

 the Upper Trias, there are P7iolidophorus-s\m^ed fishes (Pholido- 

 pleurus) with scales and fins almost identical with those of Belono- 

 stomus, and further discoveries elucidating the osteology of these early 

 types will be awaited? with interest in connection with the problem 

 under consideration. 



EXPLANATION OF THE PLATES. 



Plate LIV. 



Pig. L Belonostomus comptoni ; remains of head and trunk, coiled up in nodule. 

 Upper Cretaceous, Serra de Araripe, North Brazil, c.o., circumor- 

 bitals ; op., operculum ; orb., orbit ; -p.op., preoperculum ; pd., pectoral 

 fin ; s.cl., supraelavicle ; s.c, suborbitals ; s.op., suboperculum. [47892.] 



Plate LV. 



Fig. 1. Belonostomus comptoni \ svi^mov asr^wi oi vosiYum. Upper Cretaceous, 

 Serra de Araripe, Nortli Brazil. [15495 c] 



2. Ditto ; transverse section of rostrum. Ibid. [15495 «.] 



3. Ditto ; right byomandibular, outer aspect. Ibid, p., articular process 



for operculum. [15495 5.] 



4. Ditto ; upper poi-tion of operculum, showing ornament. Ibid. 



[15495 a.] 



5. Ditto ; vertebral centra, (a) lateral aspect of caudals, (6) abdominal in 



longitudinal section. Ibid. [P. 975 <?.] 

 G. Ditto; inferior lateral scale, restored. Ibid. 

 7. Ditto ; dorso-lateral scale. Ibid. [P. 3809.] 



' Smith Woodward, " A Synopsis of the Fossil Fishes of the English Lower 

 Oolites," Proc. Geol. Assoc, vol. xi. (1890), pp. 295, 290. 



