FISHES OF PENNSYLVANIA. 3 

in the end. As it is found in shallow water and will not usually relin- 
quish its hold on the bottom, its capture is easily effected. 
3. Petromyzon concolor Krrrtianp. 
The Silver Lamprey. 
The silver lamprey belongs to the sub-genus Jchthyomyzon of Girard. It has the 
tooth on the front of the tongue divided into two portions by a median groove and the 
dorsal fin continuous but deeply notched. The maxillary tooth is bicuspid; the teeth 
on the disk are in about four series and all small. The tooth-bearing bone of the 
lower part of the mouth has seven cusps. The head (from tip of disk to first gill-open- 
ing) is two-fifteenths of the total length ; with the gill-openings its length is contained 
four and three-fourths times in the total. There are fifty-one muscular impressions 
from gills to vent. The body is rather stout, compressed posteriorly. The head is 
broad and the buccal disk large with its edges not conspicuously fringed. Color 
bluish-silvery, sometimes with blackish mottlings. Above each gill-opening there 
is a small bluish blotch. : 
The silver lamprey or mud eel is found in the Great Lake region and 
the Ohio and Mississippi valleys. It grows to a length of twelve inches 
and is usually found in deep water, but runs up the small streams to 
spawn in the spring. It is a troublesome parasite on the lake sturgeon, 
the paddle-fish, yellow perch and some other species. It becomes fixed 
to the skin by means of its suctorial disk, and the irritation of its teeth 
sometimes causes deep ulcers at the point of attachment. This lamprey 
has the same peculiarities of development as the sea lamprey and some- 
times remains in the larval condition, blind and toothless, until it has 
reached a length of eight inches. 

Ciass PISCES. Tue Fisuss. 
Suspctass TELEOSTOMI. THe True Fisues. 
ORDER SELACHOSTOMI. THE PADDLE FISHES. 
Famiry POLYODONTID. 
Genus POLYODON (Lacéripr) Brocu anv Scuyeren. 
4. Polyodon spathula Watpavm. 
The Paddle Fish. (Figure 18.) 
The body of the paddle-fish is fusiform with the snout much produced, spatula- 
like. Body scaleless, covered with smooth skin. Mouth broad, terminal, somewhat 
resembling that of a shark. Teeth in jaws very numerous and fine, deciduous. 
Spiracles with a minute barbel. The operculum is rudimentary, its flap of skin long, 
reaching almost or quite to the ventral fins. Pseudobranchiz absent. Gill-arches 
five, the last rudimentary ; gill-rakers long and ina double series on each arch. Gill 
membranes connected, free from the isthmus. Nostrils double, situated at base of 
blade. A continuous lateral line from upper portion of head along dorsal outline to 
tail. Eye small, directed downwards and tothe side. Dorsal and anal fins far back, 
