3. PETEOMYZONTID^E LAMPETRA. 7 



several instances need verification, especially in regard to the lingual 

 dentition. (Petromyzontidce Gunther, viii, 499-509.) 



* Second dorsal contiuuous with the caudal. 



a. Maxillary tooth single, forming a crescent-shaped plate, with a distinct cusp at 

 each end, between which is sometimes a median cusp. 



b. Dorsal fins two, well separated (lingual teeth pectinate) LAMPETRA, 4. 



l)b. Dorsal fin continuous, merely emarginate (lingual teeth obscurely tricuspi- 

 date) AMMOCCETES, 5. 



act. Maxillary tooth double or triple, composed of two or three pointed cusps, close 

 together, not forming a crescent-shaped plate (lingual teeth in two 

 pairs, the posterior pair at least pectinate). 



c. Dorsal fin continuous ICHTHYOMYZON, 6. 



cc. Dorsal fins entirely separated PETROMYZON, '/. 



4. LAREPETRA Gray, 1851. 

 Lamperns. 



(Gray, Chondropterygians, 140: type Petromyzon fluviatilis L.) 



Lampreys of rather small size, with the maxillary tooth single, devel- 

 oped as a broad crescent-shaped plate, with a cusp at each end of it, the 

 two separated by a broad interspace, in the middle of which is some- 

 times a smaller cusp. Dorsal fin divided by a deep notch, which breaks 

 the continuity of the fin; second dorsal connected with the caudal; 

 mandibulary plate well developed, the number and arrangement of its 

 teeth varying with the species; lingual teeth finely pectinate; lips 

 usually conspicuously fringed. The species are little known. One of 

 them, _L. flumatilis, is European, and is closely related to L. plumbea; the 

 other described species are American. (Latin, lampetra, a lamprey, 

 from lambere, to suck ; petra, stone.) 



* Maxillary tooth tricuspid, a small median cusp being present; mandibulary cusps 



comparatively few and weak. (Entosplienais Gill.) 

 t Mandibulary plate with five cusps, the middle ones smaller. 

 t Lips fringed with conspicuous papillae. 



4. JL. ta'adeaitata (Gairduer) J. & G. Three-toothed Lamj>rey. 



Lips thick, fringed with numerous papillae, each papilla standing in 

 the middle of a little circular depression having a raised margin, which 

 is partly concealed by a rugose tessellated plate investing the inner 

 surface of the lips, and of the same horny nature with that which forms 

 the outside of the teeth; both are softened and peel off in spirits. Four 

 small, acute, conical teeth stand in a row across the upper part of this 

 plate, and four larger ones occupy each of its sides, the upper and lower 

 pairs being bicuspid and the middle ones tricuspid ; these stand on the 



