280 North American Species of Pelromyzoniid®. 



and infroral plates or lamina? destitute of odontoid tubercles, the 

 armature of the lamprey type being obsolescent." 



This genus is probably valid, unless its characters be due to 

 mutilation; as the "teeth" in all lampreys are readily lost in 

 badly preserved examples. 



Genus I.-BATH1IMYZOX Gill 

 Bathymyzon Gill, Proc. U. S. Nat. Mus., 1883, 254 (bairdi). 



1. BATHYMYZON BAIRDI. 



Petromyzon (Bathymyzon) bairdi Gill, Proc. U. S. Nat, Mus., 1883, 254 (Gulf 



Stream, Lat. 49°, at a depth of 520 fathouisV 

 Bathymyzon bairdi Jordan, Cat. Fish. Waters N. A., 1885. 4 :copied). 



Habitat. — Bassalian fauna of Atlantic. 



This species has not been described, further than that it is 

 "closely related to P. marinus." 



Genus 2.-PETROMIZOi\. 



Petromyzon (Artedi) Linnaeus, Systema Naturae, Ed. X., 1, 1758, 230 



{marinus). 

 Ichthyomyzon Girard, U. S. Pac. R. R Expl., 1858, 381 (castaneus ; 



hirudo, etc.). 

 Scolecosoma Girard, U. S. Pac. R R Expl., 1858, 385 (concolor, etc. \ 



ANALYSIS OF SPECIES OF PETROMYZON. 



a. Anterior lingual tooth divided into two by a median groove ; dorsal fin 

 continuous, with a broad notch ; fluviatile species of small size. 

 (Ichthyomyzon Girard.) 



b. Supraoral lamina (maxillary tooth) tricuspid ; some of the lateral teeth 

 bicuspid. Intraoral lamina (mandibular} 1 " plate) with 7 to 12 

 cusps ; head 9 in length. _'_'... Castaneus, 2. 



bb. Supraoral lamina bicuspid ; intraoral lamina with 7 cusps ; teeth on 

 disk in about four concentric series ; all of them simple ; origin of 

 dorsal nearly midway between tip of snout and end of tail ; body- 

 more compressed than in other lampreys ; head 1\ in length ; depth 

 12 ; 51 muscular impressions between gill-openings and vent ; color 

 silvery, bluish above, often mottled ; a small bluish spot above 

 each gill-opening, usually conspicuous even in the larvae ; similar 

 spots scattered along sides of back. - - - Concolor, 3. 

 aa. Anterior lingual tooth with a deep median groove and terminating in an 

 incurved point ; dorsal fin divided ; species of large size, anadro- 

 mous (Petromyzon). 



