38 NATURAL HISTORY. 



of the human body. The auditory apparatus is well developed in all the Rays, and the eyes are more 

 complex than those of Sharks. They are always placed on the top of the head, are directed sideways, 

 are placed at some distance from each other, and are defended by a cartilage above, behind which 

 there is usually a row of spines. Below the cartilage is an eyelid, which is capable of covering the 

 pupil. The pectoral fins have a general resemblance to those of the Monk-fish, or Angel Shark. As 

 the rays which compose the fin extend outward, they subdivide and become jointed, and in the 

 common Thornback number eighty-two, and have twenty joints between their origin and outward 

 termination. The ventral fins almost form a continuation, of the pectoral fins. The claspers of the 

 male are long and strong, and have joints which allow them to be moved in almost any direction. 

 They are placed just in front of the inner side of the ventral fins. Rays have no anal fin. There 

 are usually two small dorsal fins. All the Skates lay eggs, which are contained in a case or purse, 

 which closely resembles that of oviparous Sharks. In the embryo the tail is relatively longer 

 than in the adult, but Couch remarks that by a process not unlike that which deprives the 

 tadpole of its tail, the part of the body which lies behind the dorsal fins gradually ceases to be 

 nourished, and diminishes in size. 



The Rays form the second subdivision of the Plagiostomous fishes, and compose the section 

 Batoidei. They have been subdivided into six families by Dr. Gunther. Most of these fishes feed 

 on small crabs and shell-fish, for the mastication of which their flat teeth are well suited. 



FAMILY I. THE PRISTID.E. 



This family, like the Pristiophoridse, is distinguished by the same characteristic of an exceedingly 

 long flattened snout, armed along each edge with a series of strong teeth, much like a rough saw, 

 so that it closely resembles the last group of Sharks. The skeleton of the saw consists of three, 

 four, or five hollow and somewhat cylindrical tubes, which taper towards the end, and are 

 encrusted with a granular osseous layer, such as is usual in the bones of this group of animals. 

 These tubes are the greatly elongated and enlarged cranial cartilages, which are prolonged forward in 

 Sharks and Rays to form the ordinary rostrum or snout, though, as a rule, those cartilages vary in 

 number from one to three. The teeth are implanted in sockets, and have square bases.. It is needless 

 to remark that these teeth of the Saw-fish have no relation to the ordinary dentary armature of the 

 jaws, but rather correspond to the scales or tubercles of the skin, which are here implanted and 

 developed so as to closely simulate teeth. There are five species of the genus Pristis. They agree in 

 having the body depressed and elongated. The gill-openings are on the under side of the head, are 

 moderately wide, and placed between the pectoral fins. The nostrils are also on the under side of the 

 head ; the teeth are minute and blunt. There are wide spiracles or blow-holes behind the eye, and 

 the eye has no nictitating membrane. The pectoral fins have the front margin free, and ara placed 

 behind the head. The species are widely distributed in tropical seas. The dorsal fin. is sometimes in 

 advance of the ventral, as in Pristis perrotteti, sometimes opposite the ventral, as in Pristis pectinatus 

 and Pristis antiquorum, in both of which species the caudal fin has no lower lobe. Pristis cuspidattts 

 has the dorsal fin entirely behind the ventral, and in this East Indian species the rostrum is toothless 

 towards its base. The number of pairs of teeth in the saw varies in this species from twenty-five to 

 thirty-four, the number apparently altering with age. In Pristis antiquorum the number of pairs of 

 teeth varies from sixteen to twenty, and the teeth have the cutting edge in front only. The longest 

 Saws in the British Museum have a length of five feet, and belong to this species, which is common 

 in the Atlantic and Mediterranean ; those of Pristis zysron, from Amboyna and Ceylon, are equally 

 long. 



FAMILY II.-RHINOBATID2E. 



This family includes three genera, which have the body moderately expanded, with 

 the rayed portion of the pectoral tin stopping short of the snout. The tail is strong and 

 elongated, and carries two well- developed dorsal fins; but the caudal fin sometimes wants the 

 lower lobe. The family includes three genera. Rhynchobatus has the nostrils forming 

 oblique wide slits on the under side of the head. The two species range from the Indian Ocean to 

 the China Sea. In Rhinobatus the cranial cartilage is prolonged into a long rostrum ; the space 

 between the rostrum and the pectoral fin is occupied by membrane. The depressed body tapers 



