506 rETROMYZONTIDjE. 



genus ; but it will be better to leave its creatiou to an ichthyologist 

 who will be able to characterize it from an autopsy of examples : — 



Petromyzon (?) macrostomus. 



Petromyzon macrostomus, Burmeider, Anal. Mus. Buenos Aires, pt. 5, 

 1868, Act. Soc. Paleont. p. xxxvi. 



The outer of the concentric series of teeth contains the larger 

 teeth, about twenty-four on each side. There are no teeth in the 

 circumference of the mouth. Tongue armed with three large, pointed, 

 curved teeth, the middle of which is only half the size of the others, 

 all standing on the same base. Two dorsal tins separate from each 

 other, and the second apparently separate from the caudal. 



Buenos Ayrcs. 



2. ICHTHYOMYZON. 

 Petromyzon, sp., et Ichthyomyzon *, Girard. 



Not having seen typical examples of the species referred to this 

 genus, I can characterize it only thus : — 



Dorsal fins two, separate or continuous, and the posterior con- 

 tinuous with the caudal. Maxillary lamina with three cusps, the 

 central much smaller than the lateral. 



Western coasts of North America. 



1. Ichthyomyzon tridentatus. 



Petromyzon tridentatus, Ilichnrds. Faun. Bor.-Amer. Fish. p. IJOo. 



ciliatus, Ayrcs, Proc. Cal. Acad. Nat. Sc. 1854, p. 44 ; Girard, 



U. S. Pac. B.P. Exp. Fish. p. 378. 

 lividus, Girard, I. c. p. 379. 



" The thick obtuse lips are furnished with a circular row of small 

 nipple-like papillse, about fifty-six in number, each standing in the 

 middle of little circular depressions having a raised margin, which 

 are partly concealed by a rugose, tessellated plate, investing the inner 

 surface of the Ups, and of the same horny nature with that which 

 forms the outside of the teeth ; both are softened and peel off when 

 the specimen is kept immersed 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 upper and lower pairs being 

 bicuspid, and the middle ones tricuspid : these stand on the sides of 

 the maxillary ring, or inner orifice, and have their ends turned 

 towards it ; the inferior margin of this orifice is armed ivith a sVajhthj 

 curved dental piece, having jive acute points or teeth \fJie outer being 

 larger than the three middle], and opposite to it, on the uppers!' I e of 

 the orifice, is another piece, having two large, acutely coniccd lateral 

 teeth, with a smaller centred one. The tongue is also clothed with a 

 horny-looking substance, which is edged anteriorly by a row of 

 about twenty fine teeth. 



" The dorsal fius rise in even curves, which are highest in the 



* The generic n;nne " Enfosphemis, Gill," is not accompanied by a diagnosis. 



