TEREBELLA. 209 
3. TEREBELLA OSTREX.—Plate XXVI. Fig. 10. 
From what has been said above it may be inferred, as it is also ex- 
plained in detail, that if the generic name, Terebella, is truly meant to 
signify a creature endowed with the faculty of penetrating rocks, the 
quality is not enjoyed by those described, therefore such a characteristic 
name is misapplied. 
Nevertheless there is one exception, a very small animal, bearing 
some remote kindred to the Terebella, which seems capable of forming 
an enlarged cavity for its own lodgement in so hard a substance as shell. 
If here denominated it is provisionally, first, to shun the multipli- 
cation of genera ; next, for the purpose of recognition. 
While inspecting the exterior of old oyster shells, the observer may 
sometimes see several slender brownish tentacular organs playing around 
a fixed point, and occasionally withdrawing from view. On separation 
of the laminze, and breaking down the shell, an animal, from which they 
proceeded, is discovered lurking in a cavity amidst its solid substance. 
In some respects this animal bears considerable analogy to the Tere- 
bella. It is of vermicular form, the body extending about nine lines, 
composed of numerous segments, and with obtuse extremities, tapering 
from the middle to each side, and is bordered throughout by a row of 
pencils, composed of three or four bristles ; fewest are next the head. 
The mouth is a cavity in the anterior extremity, somewhat behind which 
are eight round flexible tentacular organs, situated on the neck. They 
are susceptible of being flattened and folded longitudinally, like those of 
the Terebella. Hight seem the peculiar complement, and they are pos- 
sibly developed in succession. Specimens, extending only two lines, had 
a single pair. A red internal, flexuous, contracting and dilating vessel, 
is near the surface, towards the upper part of the body, and is most conspi- 
cuous in young specimens. The colour of adults is very dark umber, al- 
most black, the posterior extremity and tentacula dull yellow. The 
young animal is yellowish. 
The organization of this creature is certainly modified by age. 
2D 
