TILE LAMPREYS. 143 



The orbit in this genus is generally formed by a complete bony ring. Certain fishes have been 

 described under the name Leptocephalus, which Dr. Giinther regards as larval forms, for they have 

 the notochord unossified and the eye large, and other evidences of imperfect development. It would 

 hence appear as though some of the Congers passed through a sort of metamorphosis, and this condi 

 tion. may characterise the genera Myrus, Ophichthys, and Murjena. In these fishes there is never any 

 trace of reproductive organs, no air-bladder, the vent cannot always be discovered, the stomach has a 

 large blind sac, and the straight intestine runs close to the abdominal surface. When any ossifications 

 occur they are always towards the end of the vertebral column. There are no ribs ; the skull is 

 cartilaginous; but both jaw-bones sometimes contain a little bony matter. Gelatinous substance 

 usually occurs between the muscles and the notochord, and the same substance divides the lateral 

 muscles from each other. The forms with a cylindrical 



body have red blood, but those with a fiat body JS^bT^ 



have the blood but faintly coloured. 



FAMILY XXIX. PEGASID.E. 



This family is represented by the one genus V 

 Pegasus, a group of small sea-fishes from the Indian 

 and Australian seas. It may belong to the Acanthop- 

 terygii, for the body is entirely covered with bony 

 plates, which are blended together on the trunk, but 

 form rings on the tail, and they resemble the Cata- 

 phracti in this and other characters. The plates on 

 the tail are movable. The gill-cover is a large plate PEGASUS DRACOMS. 



formed of the opercular bones blended together, 



though the inter-operculum is a delicate bone lying below it. The snout is greatly elongated ; the 

 mouth is toothless. The bony ring below the eye is well developed. The vertebrae are thin, and 

 there are no ribs. The pectoral and ventral fins, Dr. Giinther remarks, have more of the 

 Acanthopterygian than Physostomatous character. They are from India, China, and the Australian 

 coasts. 



DIVISION III CYCLOSTOMATA * (FISHES WITH A CIRCULAR MOUTH). 



The third great division of fishes is a small one, much lower in organisation than the groups 

 which have been already described, and belonging to an altogether distinct type. The vertebral column 

 is represented by a notochord, upon which the skull is not movable. The whole skeleton is carti- 

 laginous, and there are neither ribs, jaws, nor limbs. The mouth is margined by a circular lip, and 

 is suctorial. The intestine is straight, without appendages of any kind. The form of the gills has 

 suggested the name Marsipobranchii for this order of fishes, for they are pxirse-like organs, with 

 a number of lateral apertures which somewhat resemble the gill-openings of Sharks, except that 

 they are usually small and more or less circular. The heart is formed on the plan usual in fishes, 

 but the bulbus arteriosus was long overlooked, and its existence is sometimes denied. The brain 

 is small and fish-like, and quite distinct from the spinal cord. The nostril is a single tube in 

 the middle line of the head. 



ORDER MARSIPOBRANCHII. t 



FAMILY I. PETEOMYZOXTID^E. 



The fishes of this family are commonly known as Lampreys. They have the body shaped like 

 that of an Eel, are naked, and undergo a sort of metamorphosis. The larval form was long supposed to 

 be a distinct fish, and named Ammocoetes. The head is then very small, the upper lip is semicircular, 

 and the lower lip, which is separate, is small, and the mouth is toothless and surrounded by fringed 

 barbels ; the eye is small and hidden in a groove. The vertical fins extend round the body as a 

 continuous fringe. It is not till the third or the fourth year that the fishes undergo the 

 * kvktos, circle ; stoma, mouth. t marsipos, pouch ; branchia, gills. 



