LEPIDOGANOIDEI 



137 



moderate-sized fins, the dorsal, D, being single, and opposite 

 the interval between the anal, A, and ventral, V, fins : each 

 fin has an anterior spine ; the fore-part of the head is obtuse. 



Fig. a. 



Palceoniscus (Permian). 



In the Palceonisci from the coal formations at Burdie House, 

 near Edinburgh, the outer surface of the scales is striate and 

 punctate, e.g., in P. omatissimus, P. striatus ; but in the 

 Palceonisci of other British localities, and of the continental 

 and American coal formations, the scales are smooth, e.g., in 

 P. fultus, from North America, P. Duvcrnoyi and P. minutus, 

 from the coal beds of Miinster Appel. In the Palceonisci from 

 the Permian copper schales and zechstein, the scales are striate 

 or punctate : the Palceoniscus Frcicslcbcni is the most common in 

 these beds, and was the first recognized species of the genus. Of 

 this there are now forty known species, chiefly from carboniferous 

 and Permian eras : one from the Keuper beds at Ptowington, 

 Warwickshire, appears to be the last 

 representative of the genus : it is 

 the Palceoniscus superstes of Egerton. 

 Amblyptcrus, with a geological 

 range like that oi Palceoniscus, differs 

 in its shorter and deeper tail, and 

 larger body-fins, which are devoid of 

 anterior spines. In fig. 52, a indi- 

 cates the outer surface of parts of two series of the rhomboidal 

 ganoid scales ; and b the inner surface of two scales, showing 

 the ridge produced at one end into a projecting peg, which fits 



h 



Fig. 52. 



Scales of Ambhjpterus striatus 



(Carboniferous). 



