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FISHES—PETROMYZONTIDA. 755 
without arterial bulb ; alimentary canal straight, simple, without ccecal 
appendages, pancreas or spleen; generative outlet peritoneal; vertical 
fins with feeble rays, continuous around the tail; naked, ecel-shaped 
animals, inhabiting all waters. (Marsipion, a small pouch or purse; 
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 
m the form of a blind sac not penetrating the palate. The former order 
is not numerous in species, and none of its members are fouud in fresh 
water, so that in the fauna of Ohio, we have to consider only 
ORDER 1. HYPEROARTIA. THE LAMPREYS. 
Marsipobranchii with the nasal duct in the form of a blind sac, not penetrating the 
palate. This order is equivalent to the single family Petromyzontidew. (Huperos, palate ; 
artios, complete or entire.) 
KFAMILY I. PETROMYZONTIDA. THE LAMPREYS. 
Buty eel-shaped, naked, sub-cylindrical anteriorly, compressed behind ; mouth nearly 
ClESMI«, Suctorial, armed with horny teeth which are simple or multicuspid, and rest on 
papilla ; of these teeth several standing behind the opening of the esophagus are more 
or less united, forming a semi-circular plate, known as tue mandibulary plate; in front 
of the opening of the esophagus are either two large separate teeth, or else two or three 
teeth coalescent into a crescent shaped plate; these are the so-called maxillary teeth ; 
eyes present, in the adult; gill openings seven, arranged in a linear series along the 
sides cf the chest; nostril above the head; lips present, sometimes fringed; dorsal fin 
with its posterior part usually continuous with the anal around the tail, the anterior 
part more or less distinctly separated by a notch ; intestines with a spiral valve; eggs 
small. 
Some species of Lamprey build large circular nests, as large az 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 eyesrudimentary. Until quite recently, these 
larval forms have been considered as separate genera. Genera five or six, 
species about twenty, found in all waters in temperate regions. They 
attach themselves to the bodies of fishes, and feed on their flesh, 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 
fresh 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. 
