26 TELEOSTOML 



dd. Vertebrae arnphiccelian (double concave); maxillary not transversely 



divided; scales cycloid HALECOMORPHI, X. 



aa. Arterial bulb thin, with a pair of opposite valves; optic nerves crossing, 



not forming a solid chiasma. (Series TELEOSTEI.) 



e. Air-bladder (if present) connected by an air-duct with the intestinal 

 canal, this persistent throughout life ; ventral fins (if present) abdomi- 

 nal, without spines, their basilar segments rudimental. (Soft-rayed 

 fishes.) (Physostomi.) 

 f. Shoulder girdle attached to the skull by means of a post-temporal bone 



(suprascapula) ; form not eel-like. 

 g. Praecoracoid arch, present. 



h. Maxillary bone imperfect, forming the base of a long barbel ; no 



subopercle nor symplectic bone ; four anterior vertebrae much 



modified, co-ossified, and with an ossicula auditus ; supraoccipitals 



and parietals co-ossified; no scales. . . NEMATOGNATHI, XI. 



hh. Maxillary bone perfect, not entering into a barbel (rarely entirely 



wanting); subopercle and symplectic bone present. 

 . Anterior vertebrae modified, co-ossified, and with the ossicula 



auditus EVENTOGNATHI, XII. 



ii. Anterior vertebrae similar to the others, separate, and without 



ossicula auditus ISOSPONDYLI, XIII. 



gg. Praecoracoid arch obsolete; anterior vertebrae not modified; parie- 

 tal bones separated by supraoccipital ; head scaly. 



HAPLOMI, XIV. 



ff. Shoulder girdle not attached to the skull; no praecoracoid arch; 

 parietal bones in contact; maxillary wanting or united with the 



palatines; form eel-like APODES, XV. 



ee. Air-bladder without duct (in the adult) ; ventral fins without basal seg- 

 ments, usually anterior in position ; spines usually present in the fins ; 

 pectoral tins not on the plane of the abdomen ; parietal bones usu- 

 ally separated by the supraoccipital. (Spiny-rayed fishes chiefly.) 

 (Physoclysti.) 



j. Shoulder girdle connected to the skull by a post-temporal. 

 k. Lower pharjmgeals co-ossified ; no spines ; ventrals abdominal ; lateral 



line on side of abdomen SYNENTOGNATHI, XVI. 



kk. Lower pharyngeals separate (or united, and the dorsal fin with 



spines.) 



I. Gills tufted; pharyngeal bones and most of the branchihyals want- 

 ing; skin with bony plates LOPHOBRANCHII, XVII. 



U. Gills pectinate (as usual in fishes). 

 m. Superior branchihyals and pharyngeals reduced in number ; 



ventrals sub-abdominal HEMIBRANCHII, XVIII. 



mm. Superior branchihyals and pharyngeals in normal development. 



n. Ventral fins abdominal PERCESOCES, XIX. 



nn. Ventral fins thoracic or jugular. 



o. Pectoral fins not pediculate, the gill openings in front of them 

 p. Bones of the jaws distinct. 



q. Cranium normal ACANTHOPTERI, XX. 



qq. Cranium twisted, so that both eyes are on the same side 

 of head; no fin spines. . . HETEROSOMATA, XXI. 



