330 Evolution and Distribution of Fishes 



The interesting transition in scale structure, from a 

 ganoid to a cycloid type, shown by the Australian genus 

 Aetheolepis, has been pointed out by Woodward, and is 

 set forth in Fig. 54, 



Fig. 54. Aetheolepis mirabilis. Scales from four surfaces of 

 the body, showing transition from ganoid (a) to cycloid (d) type, 

 (a, a') external and internal views. (After A. S. Woodward). 



The Macrosemiidae, and Eugnathidae may for several 

 reasons be treated together, and might well have been also 

 with the Semionotidae. Of the former Woodward writes 

 {i6g: Introd. XI) : "the earliest term in the series {Ophi- 

 opsis) is the most generalized, and it has the most extensive 

 range, (Upper Trias-Purbeckian) . It is indeed a distinct 

 link between the family of Macrosemiidae and that of the 

 Eugnathidae." 



The genera and even species that make up these two 

 families are largely known from the lithographic stone of 

 Bavaria, or of Ain in France, also from the Purbeck and 

 Rhaetic beds of central England, that are rich in insects, 

 freshwater molluscs, amphibians, and other indications of 

 lacustrine or land life. But the genus Petalopteryx of the 

 first family, also Neorhombolepis and Lophiostomus of 

 the second, suggest possible migrations seaward, at least 

 in their later and more evolved species. Thus Woodward, 

 after remarking that "the ganoid fishes of the Chalk, so far 

 as recognizable, are few" then goes on to record Neorhomb- 

 olepis^ Lophiostomus, and even scant remains of Belonosto- 

 mtis and Pi'ionolepis from various southern English "Chalk" 

 localities {2 ^8: '1,02). But where the remains are scant 



