FISHES — PETROMYZONTIDjE. , 155 



without arterial bulb ; alimentary canal' straight, simple, without coecal 

 appendages, pancreas or spleen ; generative outlet peritoneal ; vertical 

 fins with feeble rays, continuous around the tail ; naked, eel-shaped 

 animals, inhabiting all waters. (Marsipion, a small pouch or pur°e; 

 bragchia, gills.) 



This class is divided into two orders, the Hyperotreta or Hag-fishes, in 

 which the nasal duct is tube-like with cartilaginous rings, penetrating 

 the palate, and Hyperoartia or Lampreys, with the nasal duct developed 

 in the form of a blind sac not penetrating the palate. The former order 

 is not numerous in species, and none of its members aie found in fresh 

 water, so that in the fauna of Ohio, we have to consider only 



ORDEE 1. HYPEROARTIA. THS LAMPREYS. 



Maisipobranchii with the nasal duct in the form of a blind sao, not peuetrating the 

 palate. This order is equivalent to the single family Peiromysonlidai. (Hiiptros, palate ; 

 artios, complete or entire.) 



FAMILY I. PETROMYZONTIDiE. THE LAMPREYS. 



Hu'y eel-shaped, naked, snb-cylindrical anteriorly, compressed behind ; mouth nearly 

 c'rTilii>, suctorial, armed with horny teeth which are simple or multicuspid, and rest on 

 papilla. ; of these teeth several standing behind the op'aing of the oesophagus are more 

 or less united, forming a semi-ciroular plate, known as tue "aandibulury plato ; in froni. 

 of the opening of the cesophagus are either two large separate teeth, or else two or three 

 teeth coalesoeut into a crescent shaped plate; these are the so-called maxillary teeth; 

 eyes present, in the adult ; gill openings seven, arranged in a linear eeries along the 

 sides of the chest ; nostril above the head ; lips present, sometimes fringed ; dorsal fin 

 with its posterior part usually continuous with the anal around the ti.il, the anterior 

 part more or less distinctly separated by a notch ; intestines with a tpiral valve; eggs 

 small. 



Some species of Lamprey build large circular nests, as large as a cart- 

 wheel, a foot or two in height, sometimes raising half a foot above the 

 surface of the water. They collect these stones, of the size of a hen's egg 

 with their mouth, and are said to fashion them into circles with their 

 tail. Whether our Ohio species build conspicuous nests, I do not know. 



These animals undergo a metamorphosis, the young forms being 

 usually toothless, with the eyes rudimentary. Until quite recently, these 

 larval forms have been considered as separate genera. Genera five or six, 

 jpecies about twenty, found in all waters in temperate regions. They 

 attach themselves to the bodies of fishes, and feed on their ilesh, which 

 they scrape off with their rasp-like teeth. The marine species of the 

 genus Petromyzon reach a considerable size and are valued as food. The 

 freeh water species are, however, too small for such use. Two genera 

 are represented in Ohio. They are easily distinguished by the differ- 

 ence in the teeth. 



