3. PETROMYZONTIDiE LAMPETRA. 7 



several instances need verification, especially in regard to the lingual 

 dentition. {Petromyzontidcv Giintlier, viii, 499-509.) 



* Secoud dorsal coiitiuuous with llic caudal. 



a. Maxillary tooth single, forming a crt'scoiit-shapod plato, -with a distinct cusp at 

 each cud, between -whifh is souiet lines a median cusp. 



h. Dorsal tins two, well separated (lingual teeth pectinate) Lampktka, 4. 



ib. Dorsal lin continuous, merely emargiuato (liugual teeth obscurely tricuspi- 



date) AMMOCOiTES, 5. 



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

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

 j)airs, the posterior pair at least pectinate). 



c. Dorsal fin coni iuuous Ichthyom YZON, 0. 



ce. Dorsal tins eutiiely separated Petkomyzon, 7. 



4.— liAMPETKA Gray, 1851. 

 Lam2)enis. 

 (Gray, Chondroi^terygiaus, 140: tj\)Q Fetromyzon flmnaiiUs Ij.) 



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 snmller 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. fluviatilis, is European,' and is closely related to L. plumhca; the 

 other described species are Americau. (Latin, lanqjetra, a lamprey, 

 from lamhcre, to suck; petraj stone.) 



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



comparatively few and weak. (Entosphenus Gill.) 

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

 t Lips fringed with conspicuous papillaj. 



4« L*. traeleaitata (Gairdner) J. & G. — Three-toothed Lamprey. 



Lips tlii(;k, fringed with numerous papillte, each papilla standing in 

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

 is partly concealed hy a rugose tessellated plate investing the inner 

 sui-face of the lips, and of the same horny nature with that wliicli 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 ui)per part of this 

 plate, and lour larger ones occu])y each of its sides, the upper and lower 

 l)airs being bicuspid and the middle ones tricuspid ; these stand on tho 



