ORDER GANOIDEI. 



989 



median jugular plate ; the vertebrae are more or less completely 

 ossified ; the tail is masked heterocercal ; and the scales are thin and 

 usually cycloidal. In all cases the teeth are small and pointed. It 

 is probable, indeed, that in the Mesozoic representatives of this 

 group we have forms closely allied to the ancestors of the Teleostei, 

 and it is more than likely that future discoveries will show a com- 

 plete passage between the Ganoids, as represented by this suborder, 

 and the Teleosteans. 



Family Pachycormid^e (Microlepidoti). — According to Pro- 

 fessor Zittel, Pachycormus and its allies should be placed in this sub- 

 order, although other writers have regarded them as more nearly 

 related to the Dapediidce. In these forms the scales, although thin 

 and imbricating, are subrhomboidal, and the vertebral column is 

 very incompletely ossified. The chief genera, which are European, 

 include Pachycormus, ranging from the Lias to the Oxford Clay 

 (Middle Jurassic) ; Pndactis, from the Lower Lias ; Euthynotus, of 

 the same horizon ; and Hypsicormus, Sauropsis, and Agassizia, of 

 the Lower Kimeridgian of Bavaria. 



Family Caturid^e. — The Caturoids are a family of Salmon- 

 shaped fishes, varying greatly in size, and ranging in time from the 

 Lias to the Chalk, but especially common in the Kimeridgian litho- 

 graphic limestones. The vertebral column may be either very imper- 

 fectly or completely ossified, the tail is more or less deeply forked, and 

 the fins have fulcra. Caturus itself comprises a number of species, 

 some of which are of large size, and two of which are represented in 

 figs. 928, 928 bis. The scales are very like those of the Teleosteans, 



Fig. 928. — Skeleton of Caturus fureatus ; from the Kimeridgian of Bavaria. Reduced. 

 /, Pectoral ; v, Pelvic ; a, Anal ; c, Caudal ; d, Dorsal fin. 



but still retain the Ganoid character of an inferior layer of bone and 

 an upper one of enamel. The dorsal fin is placed immediately above 

 the pelvic. This genus ranges from the Lias to the Kimeridgian, 

 C. maximus attaining a length of three feet. Strobilodus, from the 

 Kimeridgian of England and the Continent, is a closely allied if not 

 identical genus. Other genera are Isocolum, from the Dorsetshire 

 Lower Lias ; and the Jurassic Ziodesmus, £urycormus, Oligqpieurus, 

 CEnoscopus (Attakeopsis), Macrorhipis, and sEthalion. Oligopleurus 



