3. PETEOMYZONTID^E ICHTHYOMYZON. 9 



5. AMJttOCCETES Dume"ril, 1817. 

 Brook Lampreys. 



(Duine~ril Cuvier, Eegne Animal : type Petromyzon branch-lulls L. =tlie larval form of 

 Petromyzon planerl Blocli.) 



Lampreys of small size, with the dorsal fin continuous, sometimes 

 emarginate, but never divided into two fins, the posterior portion con- 

 tinuous with the low anal fin around the tail; maxillary tooth single, 



/ t> O/ 



broad, forming a crescentic plate, with a large bluntish cusp at each 

 end, and sometimes a small median cusp ; lateral teeth very few ; tongue 

 with two broad transverse plates, each with a median cusp ; species few ; 

 our single species is scarcely distinguishable from the common "Pride" 

 or "Small Lamprey" of Europe, Ammoccetes branchialis, (///-/.c, sand; 



xoirr^ to lie.) 



8. A. EaigCB* (Raf.) Jor. Small Blade Lamprey. 



Head moderate, nearly as long as the "chest"; the mouth compara- 

 tively small; lips with a conspicuous fringe of papilhe; dorsal fin high, 

 considerably depressed in front of the vent, but not divided into two 

 fins; the posterior lobe highest; anal fin evident ; anal tube conspicu- 

 ous in the spring ; eyes moderate ; maxillary tooth with its cusps large, 

 triangular, well separated; a small pointed median cusp usually present 

 in the adult ; in younger specimens the median cusp is obsolete, and in 

 half-grown specimens the tooth forms a curved plate without distinct 

 cusps; mandibular plate curved, with eight to ten well developed sub- 

 equal tooth-like lobes; inside of it is a plate bearing three teeth; lingual 

 teeth transverse, trifid ; a plate on each side of the buccal orifice ; the 

 remaining teeth inconspicuous. Bluish black above ; silvery below. Size 

 rather small. L. G to 10. 



A small species ascending Western streams in the spring in great 

 numbers to deposit its spawn. Great Lakes, Ohio Valley, and Upper 

 Mississippi Eegiou. It is perhaps identical with the European Ammo- 

 ccetes branchialis. 



(Petromyzon niyrum Baf. Icli. Oh. 84; Jordan, 349.) 



6. ICHTlIYOMYEOtf Girard, 1859. 



Silvery Lampreys. 

 (Girard, Pac. E. E. Surv. s, 381 : type Petromyzon argenteus Kirtland.) 



Lampreys of rather small size, having the dorsal fin high and con- 

 tinuous, with only a shallow emargination ; the teeth nearly equal over 



