SUMMARY AND CONCLUSION. 143 



forms, but no exclusively Cretaceous genera. The specimens of Microdon ratlin tux 

 and Mesodon parvus from the Purbeck Beds are especially well preserved to show 

 the osteology, and a study of them has led to several new observations. 1 There 

 can no longer be any doubt as to the close relationship of these fishes to the 

 Lepido tus-\ike ganoids. 



The Purbeckian specimens of Ophiopsis and Histionotys make some additions to 

 our knowledge of the osteology of the more generalised Macrosemiidse, which 

 emphasise their affinity to the Eugnathidse. The curious development of large 

 slime-pits in the preoperculum and supratemporal bones of ffistionotus still awaits 

 explanation. If the new genus Enchelyolepis be rightly placed in the same family, 

 its very thin cycloidal scales are particularly interesting and novel. 



Besides the remains of typical Eugnathidae of Jurassic facies, one example of 

 the later Cretaceous genus Neorhombolepis is described from the Wealden. 

 Either this, however, or a nearly similar genus also occurs in the apparently 

 Lower Cretaceous estuarine deposit in Bahia, Brazil, 2 already mentioned, while 

 the closely-related Otomifla is found in the Neocomian of Mexico.* 



Amiopsis, though so closely similar to Amia, still retains the short dorsal fin 

 which distinguishes the Jurassic members of the family. It is a Cretaceous 

 genus. 



The Purbeckian Aspidorliynchvs fisheri seems to be the latest species of the 

 genus hitherto discovered. The specimens now described show much of the 

 osteology, and suggest that the supposed close relationships of the Aspidorhyn- 

 chidse to the Lepidosteidas need further examination. The Wealden remains of 

 Bt'lonostomus are unfortunately too fragmentary for discussion. 



The Pholidophoridre occur for the last time, and the Purbeckian species of 

 Pholidophorus are interesting for the strength of their fins. P. ornatus and P. 

 granulatus are especially similar to species from the Upper Jurassic Lithographic 

 Stone of Germany and France. The almost scaleless Ceramunis may be regarded 

 as a highly specialised member of the family. Some of the Purbeckian specimens 

 of Pleuropliolis are in an unusually good state of preservation, and add to our 

 knowledge of the osteology of the genus. 



Among the Leptolepidae, which are also essentially Jurassic fishes, may perhaps 

 be recognised some of the ancestors of the typical physostomous teleosteans of the 

 later Cretaceous seas. They evidently connect the more typical " ganoids " with 

 the primitive Elopidas which are so abundant in marine Cretaceous formations. 

 By a relative enlargement of the supraoccipital and otic bones in the skull, a 



1 A. S. Woodward, " Notes on the Pycnodont Fishes," Geol. Mag., [6] vol. iv (1917), pp. 385 — 

 389, pi. xxiv. 



2 A. S. Woodward, " The Fossil Fishes of the English Chalk " (Palaeont. Soc, 1911), p. 256. 



3 Otomitla speciosa, J. Felix, Palaeontographiea, vol. xxxvii (1891), p. 189, pi. xxix, fig. 3, pi. xxx, 

 figs. 3—5. 



