PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 523 



aud liugual teeth three, pectinate, the anterior deeply impressed and 

 curved back at middle, aud the posterior correspondingly curved back- 

 wards at inner anterior angles. 



ICHTHYOMYZOK. 



Synonymy. 



<] Ichthyomyzoa, Girard, Expl. and Surveys for R. E. Route to Pacific Oc.,v. 10, Fislies, 



p. 381, 1858. 

 <^ Iclitiiyomyzou sp., GUnther, Cat. Fislies, Brit. Mus., v. 8, p. 50C, 1870. 

 Petromyzon sp., auct. 



PetromyzontinoB with the suproral lamina rather contracted and tri- 

 cuspid ; iufroral lamina multicuspid ; disco-peripheral teeth numerous, 

 and in arched series (of 4-7 each) declining downwards; and of lingual 

 teeth, anterior little impressed and incurved at middle, and i^osterior 

 (shed or wanting). 



Type Ichthyomyzon castaneus, Girard. • 



AMMOCCETES. 



Synonymy. 



> Lampreda, Bafinesqtie, Analyse de la Nature, p. 94 (not described), 1815. 

 ^ Pricus, Eafinesqiie, Analyse de la Nature, p. 94 (not described), 1815. 



> Ammocojtes A. Dumeril, in Cuvier R^gne Animal [Ire ed.], t. 2, p. 119, 1817 (based 



on larval form). 

 =: Lampetra, Gi'ay, Proc. Zool. Soc. London, pt. 19, pp. 235, 237, 1851 ; List Speci- 

 mens Fish Brit. Mus., pt. 1, pp. 137, 140, pi. 1, f. 2 (montb), 1851. 

 ? Scolecosoma, Girard, Expl. and Surveys for R. R. Route to Pacific Oc, v. 10. Fislies, 



p. 379? 1858 (based on larnal form). 

 = Petromyzon, Malm, Forliaudl. Skand. Naturf. 8 mode, p. 580, 18G0. 

 Ichthyomyzon sp., Girard. 



PetromyzontiuiB, with the suproral lamina transversely extended, and 

 with two cusps, one at each end; iufroral lamina multicuspid; discal 

 teeth uniserial, broad and bi- or tri-cuspid ; peripheral teeth uuiserialj 

 and very small lingual teeth. 



EXTOSPHENUS. 



Synonymy. 



= Eutosphenns, Gill, Proc. Acad. Nat. Sci. Phila., [v. 14,] p. 331, 1862. 

 <. Ichthyomyzon, Giinther, Cat. Fishes Brit. Mns., v. 8, p. 506, 1870. 



Petromyzontiufc with the suproral lamina transversely extended and 

 tricuspid ; iufroral multicuspid ; discal teeth uniserial, broad, and bi- or 

 tricuspid ; peripheral teeth uniserial and minute ; lingual teeth two, 

 au anterior wedge-shaped, with an almost straight, finely serrate edge, 

 and a posterior horse-shoe-shaped, and with a double finely serrate keel 

 on the sides. 



