380 



U. S. P. K. K. EXP. AND SUEVEYS ZOOLOGY GENEKAL REPORT. 



4. PETEOMTZON PLUMBEUS, Ayres. 



SPEC. CHAR. Body anteriorly sub-cylindrical, somewhat deeper than broad, posteriorly compressed. Buccal disk sub-circular, 

 provided with papillar fringes upon its periphery. Head entering somewhat over eight times and a half in the total length. 

 Anterior dorsal fin much lower than the second, and separated from it by a space equal to the half of its own length ; its origin 

 being nearer the tip of the caudal than the extremity of the snout. Tail tapering into a point. Upper region of a uniform lead 

 tint; blight silvery beneath. 



SVN. Petromyzon pluritbeus, AYRES, in Proc. Gal. Acad. Nat. Sc. I, 1855, 28. 



The specimen now before us is the very one described by Dr. Ayres, from whom it was 

 obtained by Lieut. Williamson s party. 



It measures four inches and three-fourths in total length, and, being the only one so far 

 observed, it is rather difficult to say whether it is the fullest size the species ever reaches. 



At any rate it is widely distinct from P. tridentatus and more closely allied to the other now 

 known species from California and Oregon, since, like them, it is provided with tentacular fringes 

 at the periphery of the buccal disk ; a feature which has escaped Dr. Ayres notice. Another 

 very distinctive trait between this species and P. tridentatus consists in the presence of but two 

 teeth upon the transverse piece at the anterior margin of the buccal orifice. This latter feature 

 will distinguish P. plurribeus not only from P. tridentatus but also from all the other species so 

 far observed in Oregon and California. Again: the transverse piece at the posterior margin of 

 the buccal orifice exhibits eight, nearly equal teeth, whilst in P. tridentatus and P. ciliatus five 

 only are observed, the three middle ones being smaller than the outermost two. In that respect 

 it is allied to P. astori, in which six of these teeth exist, of nearly equal development. Right 

 and left of the buccal orifice may be seen a single bicuspid tooth. 



For further particulars regarding the zoological features of the present species, we refer our 

 readers to Dr. Ayres description, which was drawn up while the specimen was in a better state 

 of keeping. 



List of specimens. 



5. PETEOMYZON ASTOEI, Grd. 



SPEC. CHAK Body anteriorly sub-cylindrical, deeper than broad ; posteriorly compressed, especially at the caudal region. 

 Buccal disk sub-circular, slightly longer than broad, provided upon its periphery with tentacular fringes. Head contained a little 

 over six times and a half in the total length. Anterior dorsal fin lower than the second, and separated from it by a space less 

 than the third but more than the fourth of its own length; its origin being somewhat nearer the tip of the caudal than the 

 extremity of the snout. Inferior lobe of the caudal more developed than the upper lobe. Yellowish brown ; lighter beneath 

 than above. 



The unique specimen of this species which has come to our knowledge measures seven inches 

 in total length. Its head is somewhat longer than the chest. The branchial orifices being sub- 

 triangular, surrounded with papillar tenticles or fringes. The dentition is similar to that 

 of P. tridentatus, P. cilialuS) and P. lividus, except in the transverse piece at the posterior 



