392 Analytical Synopsis of th& Order of Squall. 



the blue sharks, and all are placed in front of the pectoral 

 Uns. 



The fiimily of the Galeorhinoidse, or blue sharks, is by far the 

 most numerous and important of the order, and alone contains 

 nearly one-third the genera and more than half of the known 

 species of living sharks. Its representatives are distributed in 

 every sea and every zone. 



The family to which the " white shark" belongs is, on the 

 other hand, very poor in numbers, there being only five genera, 

 a single one of which is represented by more than one well 

 ascertained species, and the white shark is itself the only mem- 

 ber of its group. 



The most aberrant of the sharks and the most representative 

 of, or nearly allied to, the Rays, are unquestionably the Rhi- 

 noidse. This is evident from the condition of the caudal fin and 

 the posterior portion of the vertebral column, the absence of the' 

 anal fin, the posterior position of the dorsal fins, and especially 

 the development of the pectoral and the production forward of 

 their bases, but the branchial apertures are truly lateral, and 

 situated on the sides in the clefts of the pectoral fins ; the body 

 and head are also depressed as much as in some of the Rays, 

 and the eyes are situated on the dorsal aspect of the latter. 

 On account of the peculiarities of structure of these fishes, it has 

 been recently proposed to isolate them as a sub-order. 



Having thus, it is hoped, discovered the typical and the most 

 aberrant groups of the order, it will be endeavored to approx- 

 imately arrange the other families. At the head of the order, 

 or rather as its first family, the Rhinodontoidse are placed in 

 order to establish a serial arrangement of the first families as 

 much in accordance with their affinities as possible. A serial 

 arrangement, however, rarely or never expresses the true afiini- 

 ties of families when they are diversified or complicated. Per- 

 haps the following view in which the Alopecoidse are taken as 

 the central family, might more truly exhibit at least some of 

 their relations. 



