AMPHITRITE. 249 
2. AMPHITRITE LUNA.—Plate XXXI. Figs. 12, 13. 
The larger animals are generally distinguished by prominent fea- 
tures ; those of many of the smaller are frequently equivocal. They in- 
volve us in perplexity ; yet I acknowledge that I have perhaps exposed 
myself to greater embarrassment than some others, from my reluctance to 
institute new genera if the older could receive new species. 
The subject of this paragraph, like that of the former, is placed here 
provisionally, until the genus to which it really belongs is ascertained. 
I feel doubtful whether it is an Amphitrite, though dwelling in the sea, 
or allied to a Cristatella. ; 
The higher extremity consists of forty-four or forty-six tentacula, 
crowning the body, which projects from an indurated sandy surface, 
covering old shells for about four lines. The tentacula are disposed in 
lunate or horse-shoe arrangement, resembling the higher portion of Cris- 
tatella, fourteen or sixteen occupying the interlines. A web, rising about 
a fifth up the tentacula, unites the roots of the whole. Diameter of the 
head or tentacular plume a line and a half. 
Neither cilia nor antennule are visible. The animal rises erect from 
the indurated sand, projecting the head, or hanging over the surface. 
The termination of the intestinal canal is under the middle of the inte- 
rior row of tentacula, as in the Cristatella. 
A current or circulation is carried on through the body to the very 
tips of the tentacula, which are thus discovered to be hollow or undi- 
vided. Dark particles are carried up the body in a vessel on one side of 
the stomach, introduced and conveyed to the extremities of the ten- 
tacula, from whence they are returned and carried down a vessel on the 
other side of the stomach. 
These currents run with extraordinary force and rapidity. They 
are accelerated, retarded, or suspended by short interruptions, but other- 
wise their course is incessant. The dark particles conveyed by the 
fluid are unequal in quantity, dimensions, and proximity. They are 
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