188 VERTEBRATA. 



cylindrical appendages, one on the inner edge of each ventral fin , 

 supposed to be uped as " claspers." 



Many species of this order bring forth their young enclosed in 

 horny pouches, known as sea-purses, mermaid's eggs, &c. These 

 are secreted by a gland in the oviduct. 



Among the members of this order are the shark or white shark 

 (Carcharias vulgaris), blue shark (Carcharias glaiicus), basking 

 shark (Selache maxima), dogfish (Scyllium canictila), thresher 

 (Alopias vulpes), angel-fish (Squatina vulgaris), torpedo (Tor- 

 pedo marmorata), skate {Raia batl-i), thornback (Eaia clavata), 

 sting-ray (Trygon pastinaca}, eagle-ray (Myliobatis aquila), and 

 saw-fish (Pristis antiquorum). 



The Chondropterygii, notwithstanding their high development, 

 but also accompanied by reptilian characters, are among the 

 oldest known fish. Cestracion Philippi seems to have been their 

 nearest modern representative. The fossils known as " Ichthyo- 

 dorulites " are the spiny fin-rays of these fish. 



There are two suborders : 



Gill-openings inferior BATOIDEI. 



Gill-openings lateral SELACHOIDET. 



About 300 species are known, nearly equally divided between 

 the two suborders. 



BATOIDEI (Rays). Gill-openings free, inferior. No gill-cover. 

 No anal fin. Body broad, depressed. Notochord not persistent. 

 Oviparous. 



The pectoral fin is mostly continued to the snout. The upper 

 lid is united to the eye, or absent. The teeth are flattened. 



Torpedo has an electrical organ, composed of vertical tubes on 

 each side between the pectoral fin and the head. Myriosteon of 

 Dr. Gray, which he regarded as one of the spines of an unknown 

 starfish, is one of the three or four hollow cylindrical tubes form- 

 ing a portion of the endoskeleton of the snout of the saw-fish. 

 According to Giinther, these are modifications of the toothed pro- 

 cesses of the cranial cartilage. 



EaiidcB. Myliobatida. Torpedinidce. 



Eaia (Ray, Skate). Cephaloptera. Temera. 



*Asterodermus. Myliobatis. Narcine. 



^tobatis. Torpedo (Torpedo). 

 *Rbinoptera. 

 Trygonida. 



Pteroplatea. RhinobatidcB. Pristida. 



Trygon (Sting-ray). Rhinobatus. Pristis (Saw-fish). 



