516 PISCES [CH. 



Sub-order 8. Gadiformes. Teleostei in which the pelvic fins 

 are attached to the cleithra and are jugular in position, and in which 

 the duct of the air-bladder is closed. No hard spines are developed 

 in any of the fins and the primitive caudal fin is lost and replaced 

 by a new caudal developed from portions of the anal and dorsal fins. 

 A remnant of the cranial cavity persists above the interorbital 

 septum in which the long stalks of the olfactory lobes lie. 



Ex. Gadus, Merlucius. 



Order II. Aetheospondyli. Osteichthyes in which the noto- 

 chord is surrounded and entirely suppressed by the formation of 

 opisthocoelous centra with well developed articulating surfaces. 

 The articulating surfaces are developed out of dorsal and ventral 

 intercalary cartilages which become ossified. No supra-occipital 

 bone in the skull which is otherwise well ossified. The jaws are long 

 and the maxilla represented by a series of bones. The upper jaw 

 articulates with the skull behind the orbit but is still supported by 

 hyomandibular and symplectic. Splenial and supra-angular bones in 

 the lower jaw The tail fin a rounded lobe, the body is covered 

 with ganoid scales beset with denticles forming fulcra on the anterior 

 border of the tail fin. The conus is distinct in the heart and the 

 optic chiasma in the brain. Ovary and oviduct are continuous and 

 the testis discharges through the kidney by vasa efferentia. A 

 spiral valve on the intestine. Air-bladder opens into pharynx in 

 mid-dorsal line. 



Ex. Lepidosteus. 



Order III. Protospondyli. Osteichthyes in which dorsal and 

 ventral intercalaries are present and join to form archless pre- 

 centra at least in the tail region, the arch-bearing postcentra being 

 formed from a ring connecting neural and haemal arch-pieces 

 (basidorsals and basiventrals). Both pre- and postcentra are am- 

 phicoelous. No supra- occipital in the skull which .is otherwise 

 well ossified. The jaws are short, the maxilla is a single tooth- 

 bearing bone. Splenial bone in lower jaw. A single gular plate 

 on the under side of the throat. Tail fin a rounded lobe, body 

 covered with thin cycloid scales. The conus distinct in the heart 

 and the optic chiasma in the brain. Oviduct short, opening into 

 coelom by a wide funnel. Testis discharging through the kidney 

 by vasa efFerentia. A spiral valve on the intestine. Air-bladder 

 opens into pharynx in mid-dorsal line. 



Ex. Amia. 



