CORALS OF THE CRAG. 3 
It may also be worth remarking that similar smooth and simple coste exist in all the 
species of this genus belonging to the present period or to the Miocene deposits; whereas 
the older species, found in the Eocene formation, have the costa crispate, and composed of 
series of papillee.' 
The calice (fig. la) is regularly elliptic and slightly arched, the extremities of its 
great axis being lower than those of its small axis. The proportion between the two 
diameters is nearly constant, and the form of the ellipse, represented by the calicular 
margin, is termediate between that of Sphenotrochus granulosus, which is much shorter, 
and that of Sphenotrochus Andrewianus, which is more elongated; it is approximately 
as 100: 150. The size of the calice is also subject to very slight variations in individuals 
which have attamed their definitive form, whether they be short or tall. 
The fossula is very shallow. 
The columella (figs. la and 1c) has the form of a rather thin, vertical lamina, situated in 
the direction of the long axis of the calice and of the basal edge of the eorallum. Its 
upper edge is nearly horizontal, and reaches almost to the level of the apex of the septa ; 
it is obtuse at its angles, and divided into two equal lobes by a small notch ; sometimes 
three of the lobes are visible. ‘The structure of this part of the polypidom may be very 
well shown by a vertical section corresponding to the small axis of the calice ; it is formed 
by two delicate parallel laminze, applied together, thickened near its upper edge, and united, 
towards its base, to the wall, so as to form with the mural sclerenchyma one compact 
mass. 
The septa, as im all the other species of this genus, form three complete and well- 
developed cycla (fig. la); they are consequently twenty-four im number, and they are 
closely set, straight, thick exteriorly, and becomimg gradually thinner towards the centre of 
the calice, exsert, arched at their apex, truncate at the upper end of their imner edge, and 
granulated on their surface. These granulations are easily brought to view by a vertical 
section of the corallum (fig. 1c); they are small, unequal in size, pointed, not numerous, 
and not disposed in a regular manner, excepting near the upper edge of the septa, where 
they form a curved line nearly parallel to the edge. The septa of the first and second 
cycla are nearly similar; and, as is often the case im Corals with an elliptic calice, the 
two primary septa, corresponding to the long axis of the calice, are a little smaller than 
the four others of the same cyclum, and the six secondary ones. ‘The tertiary septa are 
! The fossil Coral figured by Mr, Isaac Lea, under the name of Turbinolia nana, and mentioned by 
that author as belonging to the Eocene strata of Alabama, would appear to be an exception to this rule, 
for it resembles much the Sphenotrochus Milletianus, and seems to have smooth cost; but the figure given 
by Mr. Lea is not sufficiently explicit for us to be able to decide the question, or even to be quite sure 
that this Turbinolida really belongs to the genus Sphenotrochus, and in the text the author says that 
he could see no trace of a columella (Lea, Contrib. to Geol., p. 195, tab. vi, fig. 209). In the present state 
of paleontology, we may, therefore, consider the above-mentioned observation as still holding good; and 
the distinction between the Eocene species of Sphenotrochus and the more recent representatives of the 
same generic type is a result not devoid of interest for geologists as well as for zoologists. 
