10 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 
Ibe large buccal disk, the maxillary teeth being pointed, two in number, 
set close together, without interspace, and not forming a crescent-shaped 
plate; lateral teeth all nnicuspid; mandibulary with numerous close- 
set pointed cusps, appearing like distinct teeth ; lingual teeth in two 
series, the posterior series finely pectinate, Avith a median suture dividing 
it into a right and left crescent-shaped comb; anterior series not divided; 
the pectin® coalescent. This genus is most nearly related to Fetromyzon, 
differing chiefly in the continuous dorsal. The two known species in- 
habit the Mississippi Valley and the Great Lakes, fish; /lu'Cw, to 
suck.) 
*M;iudibulary plate with seven teeth. 
9. I. targeuatcais (Kirt.) Grcl. — Silvery Lamprey. 
Body stoutish, compressed behind; head broad, with large buccal 
disk, which is fringed, but not very conf,picuously ; teeth pretty strong 
and nearly uniform, the two maxillary teeth being very similar to those 
on the rest of the disk ; mandibulary teeth conuivent, the middle ones 
tlie longest ; upper margin of dorsal scarcely depressed in front of the 
vent. Color bluish; sides silvery, often mottled; a small dusky siiot 
above or nearly above each gill-opening, usually cousi)icuous. L. 12. 
Great Lakes and Mississippi Valley ; rather common ; ascending small 
brooks in the spring. 
{Petromyzon arycntcus Kirtlaud, Bost. Jonrn. N.at. Hist, iii, 1840, 342, with plate. — 
Ammocates concoJor Kirt. 1. c. 473, with i^late. — Ichtliyornyzon hiriido Grd. Pac. R. R. 
Siirv. 342. — Ichthyomyzon hiriido Gthr. viii, 507. — Ammoccetes aryentcus et hirudo Jordan, 
349-’50. — Ammoewtes apyptera Abbott, Proc. Ac. Nat. Sci. Phila. 1860, 327.) 
** Mandibulary plato with nine teeth. ^ 
10. I. castsiMCWS Grd. — Chestnut-colored Lamprey. 
Lips with short fringes ; dorsal fin high, with a depression in front of 
the vent. A little known sjtecies, differing from the preceding, if at all, 
in the number of teeth on the mandibulary plate. Minnesota. 
{Ichthyomyzon castaneus Grd. Pac. R. R. Surv. 381.) 
■y.— PETROITIYZOJV Linnajus, 1758. 
Sea Lampreys. 
(Artedi Linnaius, Systema Natnrje; type Petromyzon marinus L.) 
Lampreys of medium or large size, with the maxillary teeth separate, 
Itointed, and close together, not forming a crescent-shaped jdate; man- 
dibulary plate with seven to nine cusps; lingual teeth forming two 
crescent-shaped plates on each side ; first dorsal fin well separated from 
