3. PETROMYZONTIDiE LAMPETRA. 7 
several instances need verification, especially in regard to tlie lingnal 
dentition. (Petromyzontidw Giintber, viii, 499-509.) 
* Second dorsal contimious with the caudal. 
a. Maxillary tooth single, forming a crescent-shaped plate, with a distinct cnsp at 
each end, between which is sometimes a median cusp. 
1). Dorsal tins two, well separated (lingual teeth pectinate) Lampetra, 4. 
bb. Dorsal fin continuous, merely em.arginate (lingual teeth ohscurely tricuspi- 
date) Ammoccetes, 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 
pairs, the posterior pair at least pectinate). 
c. Dorsal fin continuous Ichtha’OMA'zon, 6. 
cc. Dorsal fins entirely separated Petrojiyzon, 7. 
4.— LAITIPETRA Gray, 1851. 
Lamperns. 
(Gray, Chondropterygians, 140: rdromyzon JluviaiUis 'L.) 
Lani]n-cys of rather small size, with the maxillary tooth single, devel- 
oped as a broad crescent-shaped plate, with a cnsp at each end of it, the 
two separated by a broad interspace, in the middle of which is some- 
times a smaller cnsp. Dorsal fin divided by a deep notch, tvhich breaks 
the continnity of the fin,- second dorsal connected with thecandal; 
mandibidary plate well developed, the nnmber and arrangement of its 
teeth varying with the species; lingnaH^teeth finely pectinate; lips 
nsnally conspicuously fringed. The species are little known. One of 
them, L. Jhiviatilis, is European, and is closely related to L. plumhca; the 
other described species are American. (Latin, lampetra, a lamiirey, 
from lamhere, to suck ; petra, stone.) 
* Maxillary tooth tricuspid, a small median cusp being present; maudibulary cusps 
comparatively few and weak. {Entosphcnus Gill.) 
t Mandifiulary plate with five cusps, the nuddle ones smaller. 
t Lips fringed with conspicuous papillaj. 
4. E. tR-dcleBita^ta. (Gairduer) J. &-G. — Three-tootbecl Lamprey. 
Lips thick, fringed with nnmerons papillae, each papilla standing in 
the middle of a little circnlar depression having a raised margin, Avhich 
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 u])i)er and lower 
pairs being bicuspid and the middle ones tricuspid ; these stand on the 
