ICHTHYOLOGY. 



557 



The lowest and most anomalous of all the species of Fishes, 

 is the BRANCHIOSTOMA or LANCELET, (Amphioxus lanceolatus,) 

 usually about two inches in length, and generally distributed 

 throughout the seas of Europe and North Africa. So unique is 

 the structure of this minute creature, that, on the Chart, it is 

 dissevered from the Stone-Suckers. " A vertebrated animal 

 without a brain, a fish with the respiratory system of a mollusk, 

 and the circulatory system almost of an Annelide," presents a 

 combination of characters which has challenged its right to a 

 place among the Vertebrates, and seems to justify its separation 

 from the Lampreys,, with which some naturalists have ranked it. 



The Myxines, or GLUTINOUS HAGS, of the most Northern and 

 Southern seas, are almost equally strange in form and structure, 

 having been classed by Linnaeus and other writers, among the 

 WORMS. 



Their place is filled in the higher parts of the Southern hem- 

 isphere, by the equally curious and nearly allied genus, Hepta- 

 trema.* 



The Lepidosiren, (Gr. scaly-siren,) is the connecting link be- 

 tween FISHES and Reptiles, being so dubious in its organization, 

 that its true position is disputed. Most naturalists of Continental 

 Europe consider it to be a reptile, while Prof. Owen confidently 

 maintains its claim to a place among the Fishes. If assigned to 

 the Reptiles, its position would be as a. fourth order of the Batra- 

 chians. 



Prince Bonaparte divides the Fishes into four orders, viz : 

 Acanthopterygii , Malacopterygii, Plectognathi, and Cartilaginei. 

 His arrangement is by many highly esteemed. 



Agassiz names the orders of Fishes from their scales, (his 

 classification being applicable to the fossil as well as the living 

 forms,) viz : 



(1) CTENOIDS, (from Gr. ktenos, a comb,) in which the scales 

 consist of plates whose posterior or free margin is pectinated, or 

 comb-like, as in the Perch, Bass, Pumpkin-seed, &c. 



* The name Heptatrema (meaning seven apertures or perforations) was 

 given to this genus by Dumeril. It is found, however, that the number of 

 apertures varies. Mr. C. Girard describes one of these fishes of the South- 

 ern Hemisphere, as having fourteen breathing holes. (See " U. S. Naval 

 Astronomical Expedition,'' 1 published at Washington, D. C., 1855.) He adopts 

 the generic name of Miiller, Bdellostoma, (Gr. Bdello, I suck; stoma, 

 mouth,) founded on the structure of the mouth, and calls the speci- 

 men which he figures, Bdellostoma poly trema, (Gr. many perforations.) 



