SHARKS AND SKATES. 79 



stated to attain that of seventy." It has an anal fin, two dorsals without spines, the 

 first nearly opposite the ventral ; both mouth and nostrils are near the extremity of 

 the snout, and the spiracles are very small. Of 3Iicristodus punctatus, only the jaws 

 have been examined by a scientific person. This shark is stated to reach a length of 

 twenty feet, and to be spotted ; it occurs in the Gulf of California. In both Micro- 

 stodus and Rhinodon, the teeth are very small, in the former genus the largest being 

 but little more than a line in length and very numerous. This agrees well with what 

 is reported of its habits, for it is said to feed upon Laminaria and other seaweeds, 

 a statement which, however, needs confirmation. Should this prove not to be true, 

 it will probably be found that minute marine animals constitute the food of these 

 monsters. 



The family Lamnid^ embraces a few large species of pelagic sharks, which agree 

 in the presence of an anal and two dorsal fins, the latter being without spines, the first 

 dorsal being opposite the interval between the pectoral and the ventral. The nostrils 

 are separated from the mouth, and the spiracles are minute or absent. The family 

 first appeared in the carboniferous period, and in the early tertiary almost all of the 

 existing genera were represented. 



The species of Isurus and Lamna are known as j^orbeagles. They are repre- 

 sented on our coasts by two or three straggling species, only one of which (X. cornu- 

 bicd) has been fully authenticated. The mackerel sharks of the fishermen belong 

 here, but considerable confusion exists among them. They reach a length of ten feet, 

 and annoy the fishermen not a little, by biting off their lines. Some forty or fifty 

 years ago, the oil from the livers of mackerel sharks had a commercial importance 

 and, according to Dr. Storer, one liver has been known to make eleven and a half 

 gallons of oil, and eight livers to jiroduce a barrel. At the present time, shark oil is 

 not quoted, but it is used to adulterate the cod oil used by the curriers. 



The porbeagles and mackerel sharks are sejjarated from the others of the family 

 by the moderately sized gill-openings, and the well-developed teeth, the edges of 

 which are entire. The man-eater sharks ( Carcharodoii) have the edges of the teeth 

 serrated. Of this genus, only a single species is known, C. rondeletii, but this occurs 

 in all temperate and tropical seas, though it is very rare on our coasts. The specimen 

 seen by Dr. Storer measured thirteen feet in length, but the species is known to reach 

 a length of forty feet. Notwithstanding its size, comparatively little is known of 

 this monster, and it may be that individuals exist of larger size than that just men- 

 tioned. In a specimen thirty-six and a half feet in length, the teeth measured one 

 and three quarters inches on the base, and two and a half inches on the lateral mar- 

 gin. The ' Challenger ' expedition frequently dredged, between the Polynesian islands 

 and the west coast of America, Carcharodon teeth with a base of four inches and a 

 side of five. Nothing is known of any recent species which attains anything like the 

 dimensions that this would indicate, but if the species to which they belong is extinct, 

 the position and condition of the teeth dredged shows that it must have died out at a 

 comparatively recent period. In the various rocks of the tertiary period, Carcharodon 

 teeth are numerous, and indicate, apparently, the existence of several species, some of 

 which must have reached enormous dimensions. 



The single species of Cetorhinus (Selache), C. maximus, has received the common 

 name, basking-shark, from the fact that at certain seasons it collects in large schools, 

 which lie motionless, the dorsal fins and the backs rising above the surface of the water. 

 It is one of the largest of the sharks of the North Atlantic, occasionally reaching a 



