TROCHUS. 317 
, 
position, we cannot always arrive at facts with certainty. 
My own impression is that all of them have four vibracula ; 
but, however this may be, in a generic point of view it is 
of no moment. Operculum as in 7. Cutlerianus. This is the 
minutest animal of the three, and by far the most active ; 
thus again showing, as I formerly observed in the ‘ Annals,’ 
on Cecum glabrum, that nature, as she diminishes in volume, 
usually accompanies that condition with an equivalent of 
increased energy and activity. 
The remaining species of this section that have not been 
examined are— 
T. UNDULATUS, Sowerby. 
T. undulatus, Brit. Moll. ii. p. 528, pl. 68. f. 1, 2, and pl. 73. f. 5, 6. 
This is the 7. carneus of Lowe. 
T. HELIcINUs, O. Fabricius. 
T. helicinus, Brit. Moll. ii. p. 531, pl. 68. f. 4, 5, and pl. 74. f. 10; 
(animal) pl. C.C. f. 4. 
T. suscarinatus ? Mont. et nobis. 
Helix subcarinatus, Mont. et aliorum. 
Adeorbis subcarinatus, Brit. Moll. ii. p. 541, pl. 68. f. 6,7, 8. 
We think this species, when the animal is discovered,— 
which has hitherto evaded every research, — will prove to be 
a Trochus. 
We believe that the ? Skenea costulata of the ‘ British 
Mollusca’ is only a worn 7. Cutlerianus, with the spiral lines 
rubbed smooth or faintly impressed and scarcely visible, which 
in live specimens is often the case ; the ribs across the volutions 
are only the bifurcating striz thickened by the action of the 
atmosphere; these striz prevail more or less in every speci- 
men. If the figures of the two in the ‘ British Mollusca’ be 
examined, their identity will be apparent. 
If it be objected that the preceding descriptions are weari- 
some, I admit that they are so, as a consecutive whole; but it 
is not fair thus to look at the question; each object must be 
