112 PISCES. 



Aspidorhynchus (fig. 79). In this genus the rostrum is mvich pro- 

 duced in advance of the mouth, and the predentary bone is compara- 

 tively short. The teeth are all pointed, fixed upon the pterygo-palatine 

 arcade, premaxilla, maxilla, dentary, splenial, and predentary bone, the 

 latter element showing a median series of large spaced teeth. The 

 vomer and premaxilla are fused with the base of the rostrum, but the 

 simple and slender maxilla is very loosely attached. The cheek is com- 

 pletely covered with plates, and the preoperculum is very wide at its 

 angulation. The operculum, suboperculum, and interoperculum are well 

 developed, and there are branchiostegal rays; but no gular plate has 



FIG. 79. 



Aspidorhynchus acutirostris; restoration, about one-eleventh nat. size. 

 U. Jurassic (Lithographic Stone) ; Bavaria. (From Brit. Mus. Catal.) 



* 



been observed. The vertebral centra are in the form of calcified rings, 

 narrow and separated in the young, longer and in contact in the 

 adult. The dorsal and anal fins are short-based and directly opposed ; 

 the caudal fin is forked. Three longitudinal series of flank-scales are 

 deepened, but those of the lateral line are not deeper than those below. 

 The typical species is Aspidorhynchus acutirostris from the Lower Kim- 

 meridgian (Lithographic Stone) of Bavaria, attaining a length of about 

 one metre. The earliest species, A. crassus, from the Bathonian (Stones- 

 field Slate) of Oxfordshire, is very small; so also is the latest known 

 .species, A. Jis/ieri, from the Purbeck Beds of Dorsetshire. 



Belonostomus. In this genus the rostrum is scarcely if at all 

 produced in advance of the mouth, and the predentary bone is com- 

 paratively elongated. Most of the teeth are sharply pointed, but those 

 of the very robust splenial bone, which sometimes excludes the dentary 

 from the oral border, form a tubercular pavement. The vertebral centra 

 are more completely ossified than in Aspidorhynchus, and the scales of 

 the lateral line on the flank are excessively deepened. The genus is 

 not certainly known below the Lower Kimmeridgian of Bavaria, where 

 the typical species, B. sphyrcenoides, occurs; but it ranges as far as the 

 uppermost Cretaceous, in which the species exhibit completely ossified 

 vertebral centra. The latter species have a very wide distribution, being 

 found in Europe, India, Mexico, Brazil, and Queensland. 



The Lepidosteidae are an exclusively Tertiary family, but 

 though now confined to the freshwaters of North America they 



