442 



obliquely arranged lozenge-shaped scales which are so characteristic of the genus. 

 The jaws are elongated into a beak which is twice the length of the head in the 

 long-nosed species (L. osseus), but shorter and oroader in the other species. In 

 both the beak is very well provided with teeth, there being several rows of small 

 teeth and one row of larger size. 



As in the Sturgeon, there is a hyoidean half-gill attached to the deep surface 

 of the gill-cover, but the spiracles do not open to the outside and are small in 

 size. One of the peculiarities of the skeleton is that the vertebrae instead of hav- 

 ing cup-like surfaces as in the Amia and the ordinary bony fishes are united by a 

 ball and so2ket joint, the soskefc being on the hinder surface of each vertebra. 



The remaining represent! veoF this important group, A mia calva, is of common 

 occurrence in the Great Lakes and sluggish waters southwards. In various 

 places it is known under different popular names: Lake Dogfish from its 

 voracity, Mudfish from the waters it frequents, Bowfin from the characteristic 

 long dorsal. In shape the Mudfish somewhat recalls the Shad tribe, and it is 

 perhaps to this division of the bony fishes to which it is most nearly allied. All 

 naturalists are agreed that the Amia is the leading representative of an extinct 

 transition group between the ancient Ganoid fishes and the modern Teleosts. 



From the latter, however, there are still many points of distinction ; such as 

 the completeness of the cartilaginous skull under the outside dermal bones encas- 

 ing it, the presence of a similar dermil bone between the lower jaws and of two 

 peculiar file-like structures attached to the hinder edge of the gill-opening. 



The general colouring of the MudHsh is dark olive-green above, pale below, 

 but the males are marked by a round black spot bordered by yellow at the base of 

 the caudal, which is absent in the females. 



SUB-CLASS V. TELEOSTEI. 



The general structure of the Tel costs has been described on p. 429; 

 it now remains to give some details as to the peculiarities of the various sub-' 

 divisions of the group. 



They are primarily classified into Physostomous and Physoclystous 

 Teleosts : i.e. those in which the air-bladder opens into the gullet in the adult, 

 and those where it is completely shut oft. Even in those forms where the air- 

 bladder does open by a tube into the gullet, its importance as a breathing organ 

 is quite unlike that in the Bony Ganoids, and its functions are therefore regarded 

 as being more closely related to the locomotion of the fish. Those Teleosts in 

 which the air-bladder is closed are regarded as further removed from the Bony 

 ^anoids than the others, and it is therefore desirable to treat of the latter first 



PHYSOSTOMI. 



In this division the scales are usually cycloid, and the fin-rays (with the 

 exception of one or more anterior ones, modified into defensive spines) soft. 



3 most primitive families are undoubtedly the Catfishes, Suckers and 

 Minnows, and they all agree in possessing the connection between the air-bladder 



s which ifc " 

 of a typical 



and m having the lower jaw projecting beyond the upper, and 



