298 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV. 
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situated rather nearer to the carina than to the suture. Both above 
and below the revolving ridge the shell is depressed, but it rounds out 
again at the suture. The lower sulcus, that between the carina and 
the revolving ridge, is narrower and stronger than the one above the 
latter. In proportion as these two sulci are evanescent, the revolving 
ridge is distinct or obscure, and to some extent the carina is affected 
in the same manner. Usually the upper part of one volution projects 
somewhat above the preceding one, so that the suture is well marked. 
The junction of the two volutions is sometimes more precise, in which 
case the suture is less depressed. When this occurs, and when the 
sides are unusually flat, without a distinct revolving ridge, shells have 
a rather individual expression, and they may possibly deserve to be 
discriminated as a variety. On the lower side the shell is gently con- 
vex and fegularly so, except for a shallow groove, more distinct in 
some specimens than in others, which occurs a little below the carina 
and helps to define it. The upper internal side is gently concave, by 
reason of conforming its shape to the preceding volution. 
_ This description refers to the later or mature volutions, the earlier 
ones showing considerable variation. The earliest whorls, one or two 
in number, appear to have been nearly circular and complanate, so 
that the spire was really depressed. ‘Then the shell became flattened 
on top, with a relatively deep median depression. The upper surface 
of the volutions here lay in the same plate, which was perpendicular 
to the axis of revolution. Then the upper or exposed surface became 
considerably broader, oblique, and much less strongly and sharply 
depressed. Finally, an elevation of its median or submedian portion 
into a revolving ridge gave it in the main a gently convex, instead of 
a concave, outline. It is due to the character of the early development 
that the spire is truncated on top, as 1f broken off, and owing to the 
same cause young shells are more discoidal than mature ones. 
The growth lines in some specimens extend forward from the suture 
for a short distance, bending backward with a sharp turn on the little 
shoulder, which occurs just below the suture. In others their course 
appears to be backward from the start. About midway on the outer 
side, or Just above the revolving ridge, they again assume a forward 
direction, which is reversed at the carina or immediately above it. On 
the under side the lines are gently sigmoid, but more or less backward 
in general direction. Thus the aperture would have had a projecting 
outline at the carina, with a strong sinus above and a shallow one on 
the under side. The growth lines are fine and regular, becoming 
strongly fasciculate and more or less sublamellose in older volutions. 
Omphalotrochus ferrieri is extremely variable in all its characters, 
passing into types which approach more or less closely to O. conoideus. 
It is named in honor of Mr. W. F. Ferrier, who, with Mr. F. B. 
