Mr. A. S. Woodward on Atheratonia. 241 



scales, apparently by the division of each vertical series into 

 two, as suggested by appearances at the base of the dorsal 

 (lig. 3) ; and it is probable that a similar arrangement occurs 

 in connexion with the pelvic fins. Upon the sides of the 

 extremely attenuated caudal lobe the scales exhibit the usual 

 elongation of one diagonal ; but the proportions of the large 

 fulcral ridge-scales cannot be observed, owing to the imper- 

 fection of the fossil. The most remarkable feature in the 

 squamation, however, is the enormous development of the 

 ridge-scales along the entire extent of the dorsal margin. The 

 series commences immediately at the back of the head and 

 comprises sixteen or seventeen scales as far as the dorsal fin ; 

 and thongh there is a diminution in size behind the dorsal, 

 they still maintain relatively large proportions. Each of 

 these scales is saddle-shaped, being very slightly arched from 

 side to side ; there is considerable overlapping, and the exter- 

 nal surface is ornamented with fine ridges, mainly disposed 

 in an antero-posterior direction. 



Determination. 



The family relationships of the fish thus described are so 

 obvious as to require no detailed discussion, and its generic 

 afiinities are likewise readily determinable. In the appear- 

 ance of the scales, the situation and proportions of the fins, 

 and the recognizable features of the head, this South-African 

 fish most nearly approaches GyroJejns *, from the European 

 Trias and Rha?tic, and Rliahdolepis '\ , ftom the European 

 Lower Permian. That it is, however, generically distinct is 

 indicated by the enormous development of the dorsal series of 

 ridge-scales ; and as it seems appropriate to employ the name 

 of the discoverer of the first tolerably complete specimen, the 

 genus may be briefly defined as follows : — 



Atheestonia. 



Trunk robust ; mandibular suspensorium very oblique and 

 gape wide. [Teeth unknown.] Fins powerful, with minute 

 fulcra ; pelvic fins with an elongated base-line, the dorsal 

 arising between the pelvics and the anal, and the last-named 

 fin remote, much elongated. iScales relatively large, exter- 

 nally marked with coarse oblique striee and subdivided into 

 smaller scales at the base of the dorsal, anal, and pelvic fins ; 



* W. Dames, " Die Ganoiden des deutschen Muschelkalks," Palseont, 

 Abbandl. vol. iv. (1888), pp. 1.35-137. 



t R. II. Traquair, "Ou the Agassiziau Genera Ainhlypterus, Palceo- 

 niscus, Gp-olepis, aud Pi/ffopterus," Quart. Jouru. Geol. Soc. vol. xxxiii, 

 (1877), p. 552. 



