58 GIANT FISHES 



As in a large number of ground-living animals, coloration 

 of the upper surface of the Rays is in close harmony with 

 that of the ground on which they live, whilst the under-side 

 is usually a dead white. The skin of the upper surface is 

 generally strengthened by the presence of numerous dermal 

 denticles, which often take the form of sharp spines, and that 

 of the lower surface is quite smooth. 



The Rays may be looked upon as a comparatively modern 

 offshoot from the Sharks, the earliest forms having made 

 their appearance towards the middle of the Mesozoic Era. 

 They are nearly all sluggish, rather clumsy creatures, and 

 with few exceptions are found in fairly shallow inshore waters. 

 Some are found at considerable depths, however, and a few 

 live fairly near the surface. 



GUITAR-FISHES. 



(Family Rhinobatid^.) Fig. 25. 



Shark-like Rays, with the head and body flattened, but 

 with a thick powerful tail that merges imperceptibly into 

 the trunk. There are 2 well-developed dorsal fins and a 

 distinct caudal fin. The pectoral fins are expanded, but are 

 not continued as far forward as the snout. The pelvic fins 

 have no notch. The upper surface is covered with a uniform 

 shagreen of tiny denticles, and there are usually some larger 

 denticles, especially down the middle of the back. The 

 coloration is variable, but most of them are uniformly brown 

 or grey above. 



These rays are found in most warm seas in rather shallow 

 water. Fossil remains occur in rocks of the Jurassic and 

 Cretaceous periods, and reveal fishes extraordinarily similar 

 to their descendants living to-day. 



It is impossible to deal here in detail with the various 

 genera of Guitar-fishes, most of which have very similar 

 habits, and the family must be considered as a whole. Three 

 genera (Rhina, Rhynchobatus , Rhinobatus) , however, may be 

 specially mentioned, as these include species that grow to a 

 length of 6 feet or more. 



The so-called Mud Skate {Rhina ancylostoma) is widely 



