FISHES—PETROMYZONTIDAE—ICIITHYOMYZON. 
381 
margin of the buccal orifice, which exhibits six nearly equal teeth, in which respects it resem¬ 
bles more P. plumbeus. The eyes are large, sub-circular, and rather inconspicuous. The base 
of the second dorsal fin enters seven times in the total length, being, therefore, exactly an inch 
long. The second dorsal passes to the upper lobe of the caudal fin by a shallow and gradual 
depression. There is no trace of anal fin, and the lower lobe of the caudal is more extended, 
and posteriorly deeper than the upper lobe. The caudal itself is lanceolated, tapering into a 
point. The vent is placed somewhat posteriorly to the origin of the second dorsal fin. 
The color is yellowish brown, of a deeper tint along the dorsal region and upper surface of 
the head than beneath. 
List of specimens. 
Catal. 
No. 
No. of 
spec. 
Locality. 
When 
collected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
978 
i 
Astoria, Oregon. 
1854 
Lieut. W. P. Trowbridge. 
Alcoholic. 
Lieut. Trowbridge.. 
ICHTHYOMYZON, Girard. 
Gen. Char. —Buccal disk funnel-shaped, sub-terminal, inferior, sub-circular or sub-elliptical, fringed upon its periphery. 
Two vertical, finely denticulated jaw pieces, one on either side of the esophagus ; a similar horizontal piece below the 
former. Teeth within the buccal disk generally simple, curved, disposed upon lateral ogees, largest inwardly. Gills in 
separate partitions within the chest. One single dorsal fin united to the upper lobe of the caudal. No anal fin. 
This genus differs from Petromyzon by the form and disposition of the teeth, and by the 
presence of one dorsal fin instead of two. The horizontal jaw piece has the shape of two arcs of 
a circle soldered together, whilst in Petromyzon the same cartilaginous piece is nearly transverse. 
A rather large, tricuspid tooth, may be observed at the anterior margin of the buccal aperture, 
instead of a transverse sub-crescentic piece, armed with three distinct hooks; and at the posterior 
margin of the same aperture is a series of uniform teeth, closely set together upon an arc of a 
circle, instead of the five distant unequal teeth as observed in Petromyzon. 
To this genus belong: P. planeri, Bl. of Europe; and P. lamottenii, Lesu; P. argenteus , 
Kirtl; P. appendix , DeIyay; and the following two species. 
1. ICHTHYOMYZON CASTANEUS, Grd. 
Spec. Char.— Head depressed, constituting the ninth of the total length; body and tail compressed. Buccal disk sub- 
elliptical, provided with a double series of short, tentacular fringes upon its periphery. Posterior margin of buccal aperture 
exhibiting a series of nine teeth, disposed upon an arc of a circle. Eyes small and inconspicuous. Spiracle sub-tubular, raised 
above the surface of the head. Origin of the dorsal fin equidistant between the anterior margin of the buccal disk and the 
apex of the tail. Vent situated immediately in advance of the most elevated portion of the dorsal fin. Chesnut colored, of 
a darker tint above than beneath. 
What we have termed head is measured from the anterior extremity of the buccal disk to the 
first branchial orifice, the chest being the region occupied by the entire series, seven in number, 
of the same branchial orifices. 
The length of the head is equal to that of the chest. The tentacles, at the periphery of the 
buccal disk, are inserted into a shallow groove, formed exteriorly by the thickened edge of the 
disk, and interiorly by a soft and flexible membranous ridge. The fringes themselves are more 
developed posteriorly than anteriorly. The branchial orifices are sub-circular, provided with 
