The Ganoids 17 



Order Chondrostei. The order Chondrostei (xovdpos, carti- 

 lage; ocrreov, bone), as accepted by Woodward, is characterized 

 by the persistence of the notochord in greater or less degree, 

 the endoskeleton remaining cartilaginous. In all, the axonosts 

 and baseosts of the median fins are arranged in simple regu- 

 lar series and the rays are more numerous than the sup- 

 porting elements. T-he shoulder-girdle has a pair of infra- 

 clavicular plates. The pelvic fins have well-developed base- 

 osts. , The branchiostegals are few or wanting. In the living 

 forms, and probably in all others, a matter which can never 

 be ascertained, the optic nerves are not decussating, but form 

 an optic chiasma, and the intestine is provided with a spiral 

 valve. In all the species there is one dorsal and one anal fin, 

 separate from the caudal. The teeth are small or wanting, 

 the body naked or covered with bony plates; the caudal fin is 

 usually heterocercal, and on the tail are rhombic plates. To 

 this order, as thus defined, about half of the extinct Ganoids 

 belong, as well as the modern degenerate forms known as stur- 

 geons and perhaps the paddle-fishes, which are apparently derived 

 from fishes with rhombic enameled scales. The species extend 

 from the Upper Carboniferous to the present time, being most 

 numerous in the Triassic. 



At this point in Woodward's system diverges a descending 

 series, characterized as a whole by imperfect squamation and 

 elongate form, this leading through the synthetic type of Chon- 

 drosteidaz to the modern sturgeon and paddle-fish, which are 

 regarded as degenerate types. 



The family of Saurorhynchidcs contains pike-like forms, with 

 long jaws, and long conical teeth set wide apart. The tail is 

 not heterocercal, but short -diphycercal ; the bones of the head 

 are covered with enamel, and those of the roof of the skull form 

 a continuous shield. The opercular apparatus is much reduced, 

 and there are no branchiostegals. The fins are all small, without 

 fulcra, and the skin has isolated longitudinal series of bony 

 scutes, but is not covered with continuous scales. The principal 

 genus is Saurorhynchus ( Belonorhynchus ; the former being 

 the earlier name) from the Triassic. Saurorhynchus acutus from 

 the English Triassic is the best known species. 



The family of Chondrosteida includes the Triassic precursors 



