10 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



Ilie 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 unicuspid; mandibulary with numerous close- 

 set pointed cusps, appearing like distinct teeth ; lingual teeth in two 

 series, the posterior series finely pectinate, with a median suture dividing 

 it into a right and left crescent-shai)ed comb; anterior series not divided; 

 the pectinse coalescent. This genus is most nearly related to Petromyzotij 

 differing chiefly in the continuous dorsal. The two known species in- 

 habit the Mississippi Valley and the Great Lakes, {iz'^og, fish; /Jt6^w, to 

 suck.) 



* Maudibulaiy i)late with seven teeth. 



9. I. arg'eaiteus (Kirt.) Grd. — Silvery Lamprey. 



Body stoutish, compressed behind; head broad, with large buccal 

 disk, which is fringed, but not very conspicuouslj- ; teeth i)retty strong 

 and nearly uniform, the two maxillary teeth being very similar to those 

 on the rest of the disk ; mandibulary teeth connivent, the middle ones 

 the longest ; upper margin of dorsal scarcely depressed in front of the 

 vent. Color bluish; sides silvery, often mottled; a small dusky spot 

 above or nearly above each gill-opening, usually conspicuous. L. 12. 

 Great Lakes and Mississipin Valley ; rather common ; ascending small 

 brooks in the spring. 



(Petromyzon argenteus Kirtland, Bost. Joum. Nat. Hist, iii, 1840, 342, with plate. — 

 Ammocustcs concolor Kirt. 1. c. 473, with plate. — Ichtkyomyzon hirudo Grd. Pac. R. R. 

 Surv. 342. — Ichthyomyzon hirudo Gthr. viii, 507. — Ammocoetes argenteus et hirudo Jordan, 

 349-'50.—Ammoccetes cepyptera Abbott, Proc. Ac. Nat. Sci. Phila. 1860, 327.) 



** Mandibulary plate with nine teeth. 



10. I. castaaaeais Grd. — Chestnut-colored Lamprey. 



Lips with short fringes ; dorsal fin high, with a depression in front of 

 the vent. A little known species, differing from the preceding, if at aU, 

 in the number of teeth on the mandibulary plate. Minnesota. 



{Ichthyomyzon castaneus Grd. Pac. R. R. Surv. 381.) 



■y.— PETROMYZOJVLinnsBus, 1758. 

 Sea Lampreys. 



(Artedi Linnaeus, Systema Naturaj; type Petromyzon marinus L.) 



Lampreys of medium or large size, with the maxillary teeth separate, 

 pointed, and close together, not forming a crescent-shaped plate; man- 

 dibulary ijlate with seven to nine cusps; lingual teeth forming two 

 crescent-shaped plates on each side; first dorsal fin well separated from 



