SHARKS AND RA YS. 517 



seldom think beyond the present moment, could not be dissuaded from bath- 

 ing. A man walking in the sea up to his knees was dragged away by one 

 almost before my eyes." 



From the Carchariidce the members of the allied family Lamnidce differ by 

 the solid crowns of the fully developed teeth as well as by the absence of a 

 nictitating membrane to protect the eye. The typical re- 

 presentative of the family is the well-known porbeagle Family 

 (Lamna cornubica), a species widely spread in the seas of Lamnidce. 

 the Northern Hemisphere, where it feeds on fishes, which are 

 bolted whole. It seldom grows to more than about ten feet in length, and is 

 believed to produce its young alive. Far larger is the gigantic Carcharodon 

 rondelctii, which may attain the enormous length of forty feet, and is in 

 truth the giant of the carnivorous sharks. It has huge, flattened, triangular 

 teeth of great depth ; but as teeth of similar type, although of much larger 

 dimensions, are met with in various superficial deposits, as they are also in 

 some of the ocean abysses, it is evident that the living species is only an un- 

 worthy representative of its ancestors. It is, however, quite large enough, 

 and we may be thankful that its still more gigantic predecessors have dis- 

 appeared from the scene. Much smaller, and with a different type of teeth, 

 are the two species of the allied genus Odontaspis. Next comes the thresher 

 or fox-shark (Alopecias vulpcs), a species growing to a length of about fifteen 

 feet, and easily recognised by the excessive development of the upper lobe of 

 the tail, which forms more than half the total length of the creature. It has 

 feeble teeth, and feeds on mackerel and other fish, which it drives together 

 by striking the surface of the water with its tail, whence the name of 

 thresher. Sailors state that threshers also harass whales by jumping up in 

 the air, and dealing them sounding "whacks" with their tails in their 

 descent. But this naturalists, who are for the most part an incredulous race, 

 stoutly refuse to believe. However, we think that, as in the case of adders 

 swallowing their young, popular observation is more likely to be in the right 

 than conclusions drawn from the study of museum specimens. To the same 

 family belongs the gigantic basking-shark (Cetorhinus maximus) of the North 

 Atlantic, commonly met with off the west coast of Ireland, and attaining a 

 length of fully thirty feet. This shark, which has very minute teeth, is 

 characterised, among other features, by the small size of the anal and second 

 dorsal fins, and the large dimensions of its gill-slits. It is a somewhat sociable 

 species, floating motionless on the surface of the sea in calm sunny weather. 

 On account of the large quantity of excellent oil yielded by its liver, it is a 

 regular object of pursuit. 



Another species (Rhinodon typicus), commonly known by the same ver- 

 nacular name as the last, forms a family by itself, being distinguished from all 

 the foregoing members of the order by the terminal position 

 of the mouth, which is of huge size, and somewhat reminds Family Rhino- 

 us of an open square-topped bag. The eyes are extremely dontidce. 

 minute, the teeth feeble, and the whole body much de- 

 pressed, with the first dorsal fin relatively small, and placed behind the 

 highest point of the back, nearly above the pelvic pair. Still smaller is the 

 second dorsal, which is situated near the tail, just over the anal. In spite of 

 its huge dimensions, fifty feet or more, this shark is a perfectly harmless 

 creature. It probably feeds on small fishes and various invertebrate animals. 

 It appears to be confined to the Indo-Pacific seas, where it is common in the 

 neighbourhood of the Seychelles. 



