TELEOSTOMI. 509 
They are usually rather small fishes, with minute rhomboidal shagreen- 
like scales, and a strong spine in front of each fin, except the caudal. 
In some genera (Parexus, Climatius) there are two rows of small 
intermediate spines between the proper pectorals and the pelvics. 
d 
FIG. 303.—Outline of Acanthodes sulcatus.—After Traquair. 
é., Pectoral fins; v., pelvics.; a., anal; d., dorsal. 
Sub-Class II. TELEoOsToMI 
Fishes with more or less ossified skeletons, especially as 
regards skull, jaws, operculum, and -pectoral girdle. The 
skull is hyostylic, the jaws being supported by the hyoman- 
dibular. The pelvic girdles are usually rudimentary or 
absent. The mouth is usually terminal; the scales are in 
the majority soft and cycloid. There is always a gill- 
cover; the inter-branchial septa are much reduced; the 
gill-filaments project freely from the gill-arches. There is 
usually a swim-bladder. There are no claspers, no naso- 
buccal grooves; there is no cloaca. The fore-brain has 
a non-nervous roof. The ova are small and numerous, 
usually meroblastic, sometimes holoblastic. Fertilisation is 
usually external. 
Order 1. CROSSOPTERYGII 
Ancient forms with pectoral fins obtusely lobate and uniserial or 
acutely lobate and biserial; with scales and dermal skull bones often 
covered with enamel-like ganoin ; with a pair of jugular plates between 
the rami of the lower jaw. All are extinct except Polypterus and 
Calamoichthys from African rivers. Examples, Osteolepis (Lower 
Devonian), Holoptychius (Devonian), Megalichthys (Carboniferous), 
In Polypterus, the body is covered with rhombic ganoid scales; 
there are numerous dorsal fins; the tail is diphycercal; the pectoral 
fin has three basal pieces as in Elasmobranchs, then two rows of 
radials, and then the dermal fin-rays or dermotrichia; the air-bladder 
is double and is used in respiration, its duct opens ventrally into the 
pharynx ; the young form has an external gill on the operculum; the 
