S80 
U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
4. PETROMYZON 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; bright silvery beneath. 
Svn. — Pdromyzonplumbeus, Ayres, in Proc. Cal. 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. plumbeus 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. 
Eor 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 abetter state 
of keeping. 
List of specimens. 
Catal. 
No. 
No. of 
spec. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
977 
i 
Bay of San Francisco, Cal- 
1855 
Lieut. R. S. Williamson . 
Alcoholic.... 
Dr. W. 0. Ayres ... 
5. PETROMYZON ASTORI, Grd. 
Spec. Char. —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. ciliatus , and P. lividus, except in the transverse piece at the posterior 
