CORALS OF THE CRAG. 3 



It may also be worth remarking that similar smooth and simple costse 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 costse crispate, and composed of 

 series of papillae. 1 



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 intermediate 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 attained their definitive form, whether they be short or tall. 



The fossula is very shallow. 



The columella (figs. \a and lc)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 corallum. 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 laminee, 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 in ill the other species of this genus, form three complete and well- 

 developed cycla (fig. \a) ; they are consequently twenty-four in number, and they are 

 closely set, straight, thick exteriorly, and becoming gradually thinner towards the centre of 

 the calice, exsert, arched at their apex, truncate at the upper end of their inner edge, and 

 granulated on their surface. These granulations are easily brought to view by a vertical 

 section of the corallum (fig. \c) ; 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 in 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 



1 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 Milletianns, and seems to bave smooth coste ; but the figure given 

 by Mr. Lea is not sufficiently explicit for us to be able to decide tbe 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 palaeontology, 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. 



