TELEOSTOME FISHES. 63 



side (181). Some of the North American forms of Arthrodiran 

 fishes , such as Gorgonichthys, Dinichthys, and Titanichthys, were 

 of enormous size, some idea of which may be gathered by a 

 comparison of the mandible or lower jaw of Coccosteus (182) with 

 that of Gorgonichthys (183), 



TELEOSTOMI (Fishes with a Maxillary Upper Jaw) . 



In the Teleostome fishes the lower jaw or mandible is the same Wall- 

 morphological element of the skull (namely, Meckel's cartilage and case "• 

 related bones) as in the previous subclasses of fishes, but the 

 upper jaw, which bears usually one or more rows of teeth biting 

 against the mandibular teeth, is not the palatoquadrate cartilage, 

 but consists of bones of dermal origin called premaxilla and 

 maxilla. The upper jaw of the Teleostomi is the equivalent of the 

 upper jaw of the higher vertebrates, namely, Amphibians, Reptiles, 

 Birds and Mammals. The palatoquadrate cartilages are present 

 in the roof of the mouth, but they are reduced, and are of less 

 importance than in the first four subclasses of fishes. 



The gills are pectinate, the gill-filaments being arranged like 

 the teeth of a comb, and they are protected by a gill-cover 

 supported by opercular bones and (usually) branchiostegal rays, 

 slender curved bones supporting the lower portion of the gill-cover. 

 The skull is hyostylic, i. e. the jaw apparatus is linked to the 

 auditory region of the skull by means of the hyomandibular bone. 

 There is no cloaca and the rectum opens in front of the urinary 

 and generative aperture or apertures. The ova are usually small 

 and numerous. 



STYLOPTERYGII (Fishes with Lobed Fins). 



The Teleostome fishes are divided into three orders, the first two 

 of which differ the one from the other chiefly in the characters of 

 the paired fins. In the first order, the Stylopterygii, including 

 the Crossopterygian Ganoids of older writers, the pectoral, and to 

 a somewhat less extent the pelvic fins are f lobed ' like those of the 



