290 North American Species of Petromyzoritidm. 



Gcnu§ 3.— AMMOCCETES. 



Lampreda liafinesque, Analyse de la Nature, 1815, 94 (name only). 



Pricus Rafinesque, 1. c. (name only). 



Ammoccetes (Dumeril\ Cuvier, Regne Animal, Ed. I, 119, 1817 (branch, 

 ialis, a larval form). 



Lampetra Gray, Proc. Zool. Soc. London, 1851, 285 (fluviatilis). 



Chilopterus Philippi, Wiegmann's Archiv, 1858, 306 (larva). 



Entosphenus Gill, Proc. Ac. Nat. Sci. Phila., 331, 1862 (tridentatus : nomen 

 nud'tm\ 



Entosphenus Jordan & Gilbert, Synopsis Fishes N. A., 1883, 7 : 867 (tri- 

 dentatus). 



This genus will perhaps admit of farther subdivision, as Dr. 

 Gill has suggested, but to us, the characters distinguishing Am- 

 mocaztes and Entosphenus seem rather of subgeneric value. 



ANALYSIS OF SPECIES OF AMMOCCETES. 



a. Supraoral lamina with a well-developed median cusp which is about half 

 the length of the other two ; anterior lingual tooth wedge-shaped 

 with an almost straight, finely serrate edge ; dorsal fin divided ; 

 buccal disk moderate. Marine species of large size, anadromous 

 (Entosphenus Gill). 



b. Infraoral lamina with five or six cusps ; teeth on buccal disk mostly 



in one series ; those above mouth unicuspid, those on sides of disk 

 larger, the first and last bicuspid, the two middle ones tricuspid ; 

 those below rather small, mostly bicuspid ; space between dorsals 

 about two-fifths length of first dorsal ; head about 10 in length ; 73 

 muscular impressions between last gill-opening and vent ; color 

 plain dark brown. - - - . - - Tridentatus, 5. 



aa. Supraoral lamina with a very small median cusp or with none ; anterior 

 lingual tooth little developed, with a crescentiform dentated edge, 

 the median denticle enlarged ; buccal disk small, with the teeth few 

 and small, none of them tricuspid ; small species, mostly fluviatile 

 {Ammocoetes). 



c. Dorsal fin divided into two fins, which are separate, or joined at base 



only. 



d. Infraoral lamina with 7 cusps, the outer ones largest ; head shorter 



than thorax, 10^ in total length ; interspace between dorsals 1^ in 

 in first dorsal ; height of first dorsal half that of second ; color 

 plumbeous above, golden below. - Aureus, 6. 



dd. Infraoral lamina with 8 or 9 subequal cusps ; about three bicuspid 

 teeth on each side of buccal disk ; teeth on upper part of disk sim- 

 ple ; head 10 in length ; dorsal fins slightly connected by membrane 

 at base ; second dorsal not much higher than first, much lower than 



