142 ME. A. S. WOODWARD ON TWO GANOIDS FROM EARLY MESOZOIC 



The first eight rays are placed close together, while those succeeding 

 are more widety spaced, and the height of the fin rapidly diminishes 

 posteriorly. The anal is somewhat shorter than the dorsal, its 

 hinder end being opposite to that of the latter, bnt its commence- 

 ment is slightly further back than the front rays of the same. 

 There are about 15 rays, preceded by very distinct small fulcra and 

 the remains of larger basal fulcra, and the first eight are closely 

 approximated, while the remainder are more widely spaced and 

 much the shortest. All the rays, both of this fin and the preserved 

 fragment of the caudal, are comparatively robust, and articulated 

 similarly to those of the dorsal, and the branching is seen to com- 

 mence at a point quite near to the base. 



Scales. — The scales exhibit the vertical elongation on the flank 

 usually met with in deep-bodied Ganoids, and are strikingly similar 

 to those of certain Platysomidae (e. g. Cheirodus or Amphicentrum) 

 and Pycnodonts (e. g. Gyrodus). They are ornamented externally 

 with prominent granulations, which tend to merge and form striae 

 parallel to the margins, and the anterior border of each is thickened 

 in the ordinary " pleuro-lepidal manner " — an arrangement so well 

 known from Sir Philip Egerton's graphic description * as to require 

 no further explanation. The " lateral line " upon the trunk is distinct, 

 and extends in a gentle curve from the summit of the operculum to 

 the middle of the caudal pedicle. 



Systematie Determination. — A hasty glance at this interesting 

 fish impresses one at once with its remarkable superficial resem- 

 blance to some of the Platysomidae ; and the relative dimensions of 

 the operculum and suboperculum might also be regarded as indi- 

 cating some afiinity with that ancient tribe. One characteristic 

 feature, however, is happily preserved, by which it is possible to 

 definitely decide the question of relationship, namely, the semi- 

 heterocercal tail. This (as well as the nature of the circumorbital 

 bones) is sufficient to lead to the institution of comparisons with 

 other deep-bodied Ganoids of a more modern type, all the Platy- 

 somidae and their allies being markedly heterocercal, and we accord- 

 ingly proceed to the Dapediidse and the Pycnodonts. The latter are 

 immediately excluded from consideration by the incompleteness of 

 their opercular apparatus, which seems to consist merely of a single 

 platet, and by the absence of fulcra on their fins. The Dapediidse, 

 however, show an agreement in almost every respect. The form of 

 the body and the relations of the fins, the characters of the opercular 

 bones, and the small fulcra fringing the anterior margin of the fins, 

 are all similar; and the new South -African fossil may thus be 

 placed in this family with but little hesitation. 



Having decided upon the family position, it remains to determine 

 the genus. Dapedius, Heterostroplius, and Tetragonolepis are the 

 only hitherto recognized Dapedioids with which it seems necessary 

 to compare the fossil, and the first two of these are quite distinct 



* Sir P. Egerton, " On the Affinities of the Genus Platysomus,'" Quart. Journ. 

 Geol. Soc. vol. V. (1849), p. 331. 



t E. H. Traquair, " On the Structure and Affinities of the Platysomidae," 

 Trans. Eoy. Soc. Edinb. vol. xxix. (1879), p. 383. 



