20 . NATURAL HISTORY. 



fins or limb eacli consists of a single ray which tapers to a point, and is jointed much like a single- 

 jointed fin-ray of an ordinary fish. These limbs are attached to arches which represent, in an impei'fect 

 condition, the corresponding pectoral and pelvic girdles of osseous fishes and amphibians. 



GENUS LEPIBOSIREN. THE SOUTH AMERICAN MUD-FISH. 



Lepidosiren was discovered in the River Amazon. It so closely resembles Protopterus in 

 the form of its body that for a long time the two species were placed together in the same genus. 

 The Lepidosiren paradoxa, however, has but five branchial arches with four intervening clefts, has 

 no trace of the external branchial appendages, has no fringe to the pectoral and ventral filaments, 

 such as is seen in Protopterus, and has about fifty-five pairs of ribs. In this animal the eyes are 

 small, and the skin passes over them. The species reaches a length of three feet, and when the waters 

 dry up on the tributaries of the Amazons the fishes plunge into the mud. 



Sir Rich. Owen remarks that Lepidosiren is proved to be a fish not by its gills, nor by its air- 

 bladder, ncr by its spiral intestine, nor by its unossified skeleton, nor by its extremities, nor by its 

 eyes, nor by its ears, but simply by its nose. For the organ of smell in every fish is a shut sac, 

 communicating only with the external surface; while in every reptile it is a canal with both an 

 external and an internal opening. So that we arrive at the unexpected result that a reptile is 

 not characterised by its lungs, nor a fish by its gills. 



THE GENUS CERATODUS. 



A few years ago Mr. Gerard Krefft announced that there was still living in the rivers of 

 Queensland, in the north-east of Australia, a fish with teeth which so closely resembled those of the 

 fossil Ceratodus from the older Secondary rocks, that he was compelled to refer it to the same 

 genus. It is stated to occur abundantly in most of the rivers, and is known locally among Europeans 

 as the Flat-head. At night it is believed to leave the streams, and go out among the reeds and 

 rushes on the flats, which are left uncovered at low tide, and it is said often to be heard moving on still 

 nights on the banks of the River Mary. In some localities it goes up the river only as far as the 

 water remains brackish, but other specimens have been captured in fresh water thirty miles inland. 

 Individuals are said sometimes to reach a length of six feet. The intestines are always found crammed 

 full of dead leaves, which belong to the natural orders of plants Myrtacese and Graminse. In external 

 shape the Ceratodus has a close likeness to the Lepidosiren, except that it more nearly resembles an 

 ordinary fish, has stouter paddles, and large scales covering the body. The head is longer than it is 

 wide, but broad and flattened, with a short snout. Its upper surface is covered with a thick skin 

 pierced by small pores. The gill-cover and throat are clothed with scales like those on the body ; 

 the eye, which is small, is near to the snout ; the corners of the mouth are in front of the eyes, and 

 the lips are thick and soft. The whole body is covered with large scales, which have faint concentric 

 lines of growth, but towards the end of the tail the scales become rapidly smaller, and small scales 

 cover nearly the whole of the terminal fin. The central portions of the fin-paddles are also covered 

 with small scales. The lateral line is marked in the usual way ; from the head to the region of the 

 vent there are twenty-two lai-ge perforated scales in this line, and beyond that point there are about 

 seventeen smaller scales. In the middle region the body is encircled by eighteen or twenty rows of 

 scales, of which only one-third are above the lateral lines. The limbs, like the tail, vary a good 

 deal in appearance ; they taper to a fine point, the front pair being longer than the hinder pair, which 

 latter are given off just in front of the vent. Nearly all the skeleton is cartilaginous, but in some 

 regions of the skull the cartilage is sheathed in thin bony tissue. Dr. Glinther describes it as a 

 complete inner cartilaginous capsule, covered with an incomplete outer osseous case, to which some 

 cartilaginous elements are attached. The skeleton of the branchial apparatus is formed of fine 

 arches, and though entirely cartilaginous, is similar to that of ordinary bony fishes. The vertebral 

 column is remai-kable for retaining a condition which is usually found only in the early embryonic 

 development of the higher vertebrates, for there is no complete division of the central gelatinous 

 rod called the notochord into separate vertebrae. Upon this notochord are developed about sixty- 

 eight sets of arches, which extend above it to enclose the spinal cord, and below to support the 

 blood-vessels. Twenty-seven of the lower arches behind the head carry ribs. The teeth are fitted for 



