ite sISErr SOF OHLOs 
A. Body long and slender, eel-like ; skin smooth and slippery, wholly devoid of scales ; 
no paired fins; no lower jaw; the mouth placed in or near the center of a large, 
circular and sucker-like disc ; a single median nostril; skeleton Cartilaginous.— 
Class: MARSIPOBRANCHII (Cyclostomes). 
AA. Body variously developed, scales usually but not always present; paired fins pres-- 
ent ; lower jaw always present; nostrils never median.— 
Class: Pisces (True Fishes). 
Class: MARSIPOBRANCHII. 
Order: FHYPEROARTII. 
Family : PETROMYZONIDAE (Lampreys). 
Key to Genera. 
A. Sucker large, and furnished with numerous teeth which are in rows radiating from. 
the mouth; horny plate above the mouth short and provided with 2 or 3 teeth, 
which are placed close together.— ICHTHYOMYZON. 
AA. Sucker relatively small, and with few teeth; mouth overhung with a crescent- 
shaped, horny plate, which terminates at each end ina distinct tooth; tongue 
armed in front with a crescentic, serrated, horny plate.— LAMPETRA. 
Genus: ICHTHYOMYZON. 
Ichthyomyzon concolor (Kirtland). SILnvER LAMPREY. 
Sucking disk large, moderately fringed ; teeth strong and nearly uni- 
form; two teeth on supraoral plate; seven in the transverse row below 
mouth, the remaining teeth arranged in about four concentric circles. Dorsal 
fin arising midway from snout to end of tail, broadly notched, continuous 
with caudal; anal fin also continuous with caudal. About fifty-two muscu- 
lar grooves between gills and vent. General color bluish, sometimes 
blotched with black ; a dark blue spot’ above each gill opening. Length 
about 12 inches. 
This species appears to be distributed throughout the state, 
though nowhere very common. It ascends small brooks in spring 
to breed. McCormick mentions finding females with ripe eggs 
on May 22, in Vermillion river. The breeding date must be 
considerably earlier in central Ohio, as Messrs. Parker, William- 
son and the writer took young larve a couple of inches long in 
Big Jelloway creek, Knox County, during the latter part of May, 
1898. On the same date a large larva seven inches long was. 
taken, so the species must continue in the larval stage something 
*It has been thought best to include here also the Lampreys (Marstpobranchit) of 
Ohio, for the reason that, in the popular idea, a lamprey isa ‘‘fish.” 
