Echeneis lunata. 415 
repose these lamine ave inclined obliquely backwards, the posterior 
emerging from behind the anterior, and they lie in such close contact 
that there can scarcely be any void between them: but when the fish, 
after having attached itself by its disk requires to take the firmest hold 
of an object, it draws the lamine, by means of the muscular apparatus of 
the organ, into a direction nearly perpendicular to the surface of attach- 
ment, and retains them in that position by the triple series of teeth on 
the edge of each lamina, the spaces naturally existing between the 
lamine to the depth of about the fifth of an inch being at the same 
instant extended to their greatest capacity, and each contributing to 
form aconsiderable vacuum. So long therefore as this combined action 
is kept up, the disk remains immoveable. 
That the spare disk in the cask may be as little incomplete as possi- 
ble, I inclose for Mr. Bennett three of the bones I had removed from it, 
one answering to the spinous process of a vertebra and the others form- 
ing two of the above moveable damine. 
Before I conclude with this genus, I may notice a couple of errors that 
authours have fallen into concerning their motions. M. Risso, for example, 
describes them as lazy and slow; yet all admit that they contrive to fix 
themselves to fishes of great velocity, and in these seas they are very 
often found upon Sharks: how could they reach these, how could they 
detach themselves from their ‘* conducteurs’”’ to catch their feces (on 
which Bose asserts that they feed), and come up with them again, unless 
they were enabled to move with great speed? Some of our oldest fish- 
ermen here tell me that, although the Echeneis swims at a moderate rate 
when lounging, or going round their canoes in search of food, it will 
pursue its prey with great quickness; and to me the lengthened-conical 
form of its body, and the length and size of its dorsal, anal, and caudal 
fins, appear to be well adapted for great speed. 
Another error, as I deem it, is that the Echeneid@ swim resupinately ; 
yet prima facie, this seems improbable, and no fisherman here has ever 
observed them swimming in that position. 
There is a small Vurse in the cask, of which I sent you a specimen 
last year. I have since then detected the spiracles; they were very 
