Fishes of M. assachusetts. 551 
P. nigricans. Le Sueur. The bluish Lamprey. 
Trans. of Amer. Phil. Soc. new series, vol. i. p. 385. 
This species is generally found attached to other 
species of fishes ; it is frequently affixed to mackerel ; 
less often to cod ; and the three specimens I have 
met with, were taken adhering to haddock. From 
the largest of these, seven inches in length, the fol- 
lowing description is made: Upper part of the body, 
of a deep blue color; beneath, bluish white. Ante- 
rior third of the body, cylindrical; back of this, 
compressed ; very much so towards the tail. Head 
oval, flattened on the top; length of the head, from 
the snout to the posterior angle of the eye, to the 
length of the fish, less than one seventh. Seven 
branchial orifices, running obliquely backwards and 
downwards from the eyes. Mouth, circular; half 
an inch in diameter; surrounded by a fleshy margin ; 
armed within with numerous incurved teeth, or 
horny spines, projecting from widened bases, resem- 
bling the spines with which the Raiae are armed. 
There are three teeth in the throat ; two higher up 
than the third, which is in front of and between 
the others. In the general appearance of the teeth, 
there is great resemblance between those of this spe- 
cies and the preceding. Eyes moderate in size; pu- 
pils black ; irides silvery. Between the eyes, on the 
top of the head, a small white spot; in front of this 
Spot, a spiracle. 
The first Dorsal fin commences back of the mid- 
dle of the fish; its posterior portion is rounded ; its 
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