OCR Text |
Show 636 ON SOME UPPER CRETACEOUS FISHES. [Nov. 18, similar to the typical members of the genus of late Jurassic age, they may be regarded as proving the persistence of this somewhat specialized type during a long period and over wide areas of the earth's surface. That is a feature of some interest in the evolution of the group. But if Apateopholis he correctly interpreted in the foregoing 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 Aspidorhynchidae, 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 Hoplopleuridae, 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 Physostomous fishes ; Apateopholis, in this respect, being paralleled only by some of the highest Physoclysti. With regard to the origin of the family, the typical genera, Aspidorhynchus and Belonostomus, so far as known, appear suddenly in the Lower Oolitesl; 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 Pholidophorus-shaped fishes (Pholido-pleurus) with scales and fins almost identical with those oi Belonostomus, 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. Fig. 1. Belonostomus comptoni; remains of head and trunk, coiled up in nodule. Upper Cretaceous, Serra de Araripe, North Brazil, co., circumor-bitals; op., operculum ; orb., orbit; p.op., preoperculum ; pet., pectoral fin ; s.cl., supraclavicle ; s.o., suborbitals; s.op., suboperculum. [47892.] P L A T E LV. Fig. 1. Belonostomus comptoni ; superior aspect of rostrum. Upper Cretaceous, Serra de Araripe, North Brazil. [15495 c] 2. Ditto; transverse section of rostrum. Ibid. [15495 a.] 3. Ditto; right hyomandibular, outer aspect. Ibid, p., articular process for operculum. [15495 b.] 4. Ditto; upper portion of operculum, showing ornament. Ibid. [15495 a.] 5. Ditto; vertebral centra, (a) lateral aspect of caudals, (b) abdominal in longitudinal section. Ibid. [P. 975 c] 6. Ditto; inferior lateral scale, restored. Ibid. 7. Ditto ; dorso-lateral scale. Ibid. [P. 3809.] 1 Smith Woodward, " A Synopsis of the Fossil Fishes of the English Lower Oolites," Proc. Geol. Assoc, vol. xi. (1890), pp. 295, 296. |