94 LOWER VERTEBRATES. 



fact may partially account for this difference in tastes. Caviare is not all of equal 

 quality; in some the eggs have reached a greater or less extent of decomposition 

 before drying. The annual amount of caviare put on the market is almost incredible. 

 The Caspian fisheries alone have in one year produced over two hundred tons. The 

 size of the roes is enormous, comprising nearly a third of the weight of a ripe female. 

 Another valuable product of the sturgeon is isinglass, which is merely the dried air 

 bladders. It is prepared by cutting open the bladders and stripping the silvery 

 gelatinous skin from the rest, and drying it. 



The ancient Romans highly prized the flesh of the sturgeon, and it figured on the 

 tables at all the great feasts. It cost enormous prices, and Cicero rebuked the 

 epicures for spending such sums on a fish. As a contrast, it might be stated that at 

 the time of writing, a sturgeon sent from Newburyport to Boston could not find a 

 purchaser, no one caring for its flesh. 



The only other genus is Scaphir/ii/nchops, the shovel-nosed sturgeons, in which no 

 spiracle is jiresent, and which has a flattened spade-lilce snout, while the bony plates 

 run together on the tail. I'our species are known, three from Asia, and one {&'. 

 platyrrhynchus) from the Mississippi valley, and the western and southei-n states. It 

 reaches a length of five feet. 



The sturgeons, though without teeth, are carnivorous, feeding mostly on other 

 fishes. Their protrusible mouth and large size renders it an easy task to swallow an 

 ordinary sized fish whole. The development of the sterlet has been followed by 

 Salensky, a Russian naturalist. It follows a type in some respects intermediate 

 between the teleosts and batrachians. A large amount of yolk is present, and on this 

 the young fish lives for three weeks. The segmentation is total but irregular. In the 

 larva, horny teeth are developed on the gums and gill arches, but the}' disappear after 

 three months. The median fin is at first continuous, but afterwards becomes divided 

 into dorsal, anal, and ventral fins. 



, The family Polyodontid^ has a distribution like the last. Two genera only are 

 known ; one, Polyodon (or Spatukiria) is represented by a single species in North 

 America; the other, Psephurus, occurring in China. Both have the body naked, or 

 covered with minute, star-shaped bony plates ; the snout is very long and shovel-like, 

 being flattened horizontally, and extending to a long distance beyond the mouth; the 

 mouth is large, and provided with minute teeth in each jaw. These peculiarities are 

 referred to in the name Selachostomi (shark-mouthed) which is sometimes used for 

 the grou]). 



Polyodon spatida is the paddle-fish, spoon-bill cat, or duck-bill cat of the Missis- 

 sippi valley and the southern states. It has the paddle terminating the snout broad, 

 and forming from a fifth to a third of the total length of the fish, which may reach fi\'e 

 or six feet. It frequents the muddy bottoms, stirring up the soft ooze with its paddle, 

 and eating the worms, crustaceans, and other organisms which it contains. PsepJiurus 

 likewise contains but a single species, P. gladius, which has been found only in the 

 rivers of China. Its habits are much like those of the paddle-fish, but it is much larger, 

 sometimes reaching a length of eighteen feet. Both genera are confined to fresh water. 



Oedee IV. — PYCNODONTINI. 



The Pycnodontini (or Lepidopleurini, as it is sometimes called) is an extinct group 

 whose members ranged from the carboniferous to the early tertiary rocks. These 



