462 PISCES SUB, CLASS IILTELEOSTOMI. 



sea forms, one from the Atlantic and the other from Japanese waters. It 

 appears to be the most shark-like type, and is characterised by the long 

 slender beak, and the absence of an. appendage on the forehead of the males. 

 From the small size of the claspers in the same sex, it has been inferred that 

 the eggs are fertilised after extrusion. ; The second genus, Callorhynchus, 

 is represented by the bottle-nosed chimsera of the Southern Seas, and, to- 

 gether with the next, has an erectile spine on the forehead of the males. In 

 form it is very shark-like, with the tail inclined upwards and_vwithout a fin on 

 its upper surface ; the muzzle being of moderate length, with a cartilaginous 

 prominence terminating in a flap of skin. Chimcera, of which there are three 

 species, is less shark-like than the other two, with the extremely abbreviate 

 muzzle devoid of any appendage, arid the whip-like tail "forming a continua- 

 tion of the longitudinal axis of the body, and finned, for some distance both 

 above and below. These fishes appear to be rare and local, and are gener- 

 ally taken in fairly deep water. Little is known of their life-history, but 

 immature examples have been captured at great depths. Although some 

 writers have considered the chimseroids as degenerate types allied to the 

 Dipnoi, Dr. Bashford Dean is of opinion that they .are more nearly related to 

 the primitive sharks. If this should prove to be well founded, the autostylic 

 type of skull must have been independently acquired in the Dipnoi and 

 Holocephali, and cannot, consequently, be of much classificatory value. 



SUB-CLASS IILTELEOSTOMI. 

 BONY FISHES AND GANOIDS. 



THE passage between the modern bony fishes and the ancient ganoids having 

 been discovered to be complete, there is no possibility of assigning these 

 two nominal groups to distinct sub-classes, or even orders, and, accordingly, 

 all the fishes which come under the designation either of Dipnoi, Holo- 

 cephali, or Elasmobranchii, are now classed as Teleostomi. Indeed, the 

 terms bony fishes and ganoids, as Dr. Bashford Dean well remarks, can only 

 be used, jn a popular and convenient sense the latter to denote the old- 

 fashioned, type, with its rectangular ganoid scales and cartilaginous internal 

 skeleton,- and the former to designate the modern type, with its rounded 

 horny scales and fully calcified skeleton. The group is a very vast one, 

 including by far the great majority of existing forms, and a host of extinct 

 ones ; and the range of variation is so great that a concise definition is by no 

 means easy. All the members of the sub-class are, however^ broadly distin- 

 guished both from Dipnoi and Holocephali by the existence in the skull of a 

 movable apparatus for the suspension of the lower jaw, this type of skull 

 structure being known as the hyostylic. In the internal skeleton, calcification 

 exists to a greater or lesser degree, and membrane-bones are always present on 

 the jaws. Moreover, the membrane-bones of the pectoral girdle, like the 

 scapula and the various clavicular bones, form a chain connected with the 

 posterior region of the skull. Very important is the close crowding of the 

 gill-arches, and their complete protection by a fully-developed operculum. 

 The external skeleton, when present, consists either of rounded horn-like 

 scales, or of quadrangular bony plates. All the living forms deposit a vast 



