GANOIDEI. 163 



Tribe 2. Eajides (Skates and Rays). Plagiostomes, with flat 

 bodies ; with five gill slits opening on the ventral surface internal to 

 the pectoral fins; with complete pectoral girdle and cranial fin 

 cartilages, without anal fins. 



In consequence of the size and horizontal expansion of the thoracic 

 fins the flat body presents the form of a large disc, prolonged behind 

 into the long thin tail, which is frequently armed with spines, rarely 

 with one or two serrated stings. The mandibles are short and stout, 

 and are furnished with teeth which may be either small and conical, 

 and arranged near one another in rows, or broad and plate-like. 

 The Rays live for the most part at the bottom of the sea, and feed 

 principally on Crustaceans and Molluscs. The Torpedos have an 

 electrical apparatus between the fin cartilages and the branchial 

 pouches. By means of this organ (fig. 590) they can stun even 

 larger fishes. Many Rays reach the considerable size of ten to 

 twelve feet. 



Fam. Squatinorajidae. Pristis antiquorum Lath. Sawfish, Ocean and 

 Mediterranean ; Hliinolatus granulatiis Cuv. 



Fam. Torpedidae. Electric Kays. Torpedo marmorata Kisso, Mediterranean 

 and Ocean ; Naruine brasiliensis v. Ott. 



Fam. Eajidae. Skates and Rays. Raja clavata L. ; R. miraletus L. 



Fam. Trygonidae. Sting Rays. Trygon pastinaca L. (Pastinaca marina 

 Bell), Atlantic Ocean. 



Fam. Myliobatidae. Eagle Rays or Sea Devils. Myllobatis aguilla L., 

 Mediterranean. 



Order 4. GANOIDEI.* 



Cartilaginous and bony Fishes, with enamelled scales, or with osseous 

 dermal plates and fulcra, with muscular conus arteriosus containing 

 rows of valves; with comb-shaped gills and spiral valve in the 

 intestine. 



In former periods of the world's history this order was richly and 

 variously represented (Sauroidce, Lepidoidce, Pycnodontd), while at 

 the present day it contains only a few forms (Lepidosteus, Polypterus, 

 Calamoichthys, Amia, Acipenser, Scaphirhynchus, Spatularia), It is 

 difficult to establish the limit towards the Teleosteans, since there is 



* Job. Muller, " Ueber den Ban und die Grenzen der Ganoiden." AbJiandl. 

 dcr Berliner Akad., 1846. 



J. Hyrtl, " Ueber den Zusarnmenhang der Geschlechts-und Harnwerkzeuge 

 bei den Ganoiden. DenTischr. dcr k. Akad. der Wissenscli., Tom. VIII., Wien. 

 1854. 



Lutken, " Ueber die Begrenzung und Eintheilung der Ganoiden." Ueber- 

 setzt von Willemoes-Suhm. Palaeontographica, 1872. 



