FISHES —PETROMYZONTIDAE — PETROMYZON. 



379 



and rather thin membrane, which would constitute a kind of tube were its posterior portion not 

 divided into two free, moveable, rounded off flaps, behind -which exist a concavity, edged 

 posteriorly with a series of small papillar fringes. A tentacular-like papilla is situated more 

 inwardly, between the edges of the flaps already alluded to. 



The anterior dorsal fin is lower than the second ; its origin is somewhat nearer the extremity 

 of the snout than the tip of the caudal fin ; its base measuring less than the sixth of the total 

 length ; the intervening space between it and the second dorsal being equal to the fifth of its 

 base. The second dorsal itself, which begins in advance of the vent, is highest behind that 

 orifice. It gradually tapers away to the upper lobe of the caudal, where a shallow depression 

 marks the point of continuity of these two fins. There is no trace of anal ridge behind the 

 vent ; the lower lobe of the caudal, beginning more anteriorly than the upper, becomes also 

 deeper near the apex of the tail, which resembles a contracted spear. 



The color is olivaceous brown, rather blackish along the dorsal region, with a metallic green 

 tint over the belly ; the fins being of a dark hue. 



List of specimens. 



Locality. 



When col- 

 lected. 



Bay of San Francisco, Cal. 1856 



Whence obtained. 



Dr. \V. O. Ayres. 



Orig. 



No. 



Nature of 

 specimen. 



Collected by- 



Alcoholic.! Dr. Ayres. 



3. PETROMYZON LIVIDUS, Grd. 



Spec Char. — Body sub-cylindrical, deeper than broad, caudal region very much compressed. Buccal disk sub-elliptical, 

 fringed upon its periphery. Head contained a little over eight times and a half in the total length. Anterior dorsal fin lower 

 than Ihe second, and separated from it by a space equal to the third of its length ; its origin being nearer the tip of the caudal 

 fin than the extremity of the snout. Inferior lobe of the caudal slightly deeper than the upper. Uniform bluish black, lighter 

 beneath than above. 



This species is closely related to the foregoing one, from which it differs chiefly by the fringes 

 at the periphery of the buccal disk, and which are disposed upon a double, very crowded series, 

 rather more developed at the anterior margin, where they are also more of a flattened shape. 

 The head is nearly as long as the chest ; the branchial orifices exhibiting the same structure as 

 in P. ciliatus. The first dorsal is placed more anteriorly, else the tail is shorter, and the tran- 

 sition of the second dorsal to the upper lobe of the caudal is less gradual than in the species just 

 alluded to. The specimen described is about fifteen inches in total length. 



The color is of a uniform deep bluish black above, somewhat lighter beneath, with a greenish 

 metallic reflect. 



List of sjjecimens. 



