154 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



"Gill-coi-ers. — The gill-covers are hirge, and composed of three pieces; the anterior 

 piece small in some, as is exemplified in the C. macrolcpidolus, and in others large, as in 

 the C. communis; opening or expansion wide. 



"Nostrih. — The nostrils are double on each side, and separated by a membrane; tie 

 largest aperture near the eyes. 



"£i/€s. — The eyes in general are pretty large, a little oblong, without nictitating 

 membrane : pupil black and roundish : irides yellowish, sometimes brown, as in the 

 C. gibhodiiH. 



'^Teeth. — No teeth in the jaws, but those of the throat, on each side, are composed of a 

 range of bones, generally blunt and thick at their summits, placed in a pectinated 

 form, on an osseous, arcuated base, of which they are a component part, and some- 

 times terminate in a hooked iioint, as in the C. maculosus ; these teeth are enveloped in 

 a thick mass of whitish substance, which covers the throat, and supplies the place of 

 a tongue. 



'^Mouth. — The mouth is generally lunated; to the palate is attached a membrane. 



"Viscera. — The intestinal canal is very much developed, and it has its origin uejr the 

 throat ; the stomach, which is simple, and without plaits and curvatures, being a con- 

 tinuation of this canal, and appears to be confounded with it. The intestines make a 

 number of circumvolutions; in a specimen of the C. macrolepidoius of 16 inches 

 in length, they were 3 feet 5 inches in length. The liver is deliquescent, and soon 

 passes into oil after exiiosure to the atmosphere. The air-hlaclder is subcylindrical, and 

 divided, in most species, into two parts ; in the C. macrolepidoius, it is separated into four 

 parts. I have remarked in the intestines of these fishes river- shells of the genera 

 Lymnaa, liulimus, etc., which dwell on aquatic plants and on the rock at the bottom of 

 the rivers; these shells the Catostomi are enabled to take with their lips, which are 

 protruded forwards by means of their jaws. 



" It is necessary to remark that in all the species which I have examined there is a 

 line which runs from the nape, beneath the eyes, and another along the head, above 

 the eyes, of small orifices, for the passage of mucus, which lines are well defined 

 after the fish is dead and desiccated, but not so conspicuous wheu recent; these lines 

 Forster improperly terms sutures. I will add that some species, in a dried state, have 

 also a tuberculated appearance on the head, which tubercles are not discernible when 

 the animals are living." — (Le Sueur, Journ. Ac. JSat. Sc. i, p. 81).) 



Hypentelium Rafinesque, 1818. — "This species {_Exo(jlossnm macropterum'] distin- 

 guished by so many secondary characters may be the type of a subgenus, which may 

 be called Hypentelium, in reference to the five lobes of the lower jaw. The species 

 with a three-lobed jaw may form then another section under the former name of 

 Maxillingua." — (Rafinesque, Journ. Acad. Nat, So. p. 420, 1818.) 



Catostomus Rafinesque, 1820. — " Body oblong cylindrical, scaly. Vent posterior or 

 nearer to the tail. Head and opercules scaleless and smooth. Mouth beneath the 

 snout, with fleshy, thick or lobed sucking lips. Jaws toothless and retractible. 

 Throat with pectinated teeth. Nostrils double. Gill-cover double or triple. Three 

 branchial rays to the gill membrane. A single dorsal fin commonly opposite to the 

 abdominal fins, which have from eight to ten rays." — (Rakinesque, Ich. Oh. p. 53.) 



Decactylus Rafinesque, 1820. — "Body nearly cylindrical, abdominal fins with ten 



