A monograph of the British fossil corals - kreidefossilien.de

48 BRITISH FOSSIL CORALS.
very slightly flexuous, and presenting laterally a few large granulations. Lissephnents
simple, almost horizontal, and few in number ;
about three from the top to the bottom of
each principal septum, as may be seen by means of a vertical section. Height varying
from one to two inches ; diameter of the calice, four lines ; depth of the fossula, two lines.
The genus Parasmilia, circumscribed within the limits assigned to it
in the Introduction
to this Monograph, only contains seven species, all of which belong exclusively to the upper
beds of the Chalk Formations.
Three of them (P. centralis, P. Gravesiana, and P. ehngatd)
have already been described in our Monograph of the Astreidse,^ and the four others
(P. MantelUi, P. Fittonii, P. cylindrica, and P. serpentina) will be made known in the
present work. They all differ but little from each other, and in order to recognise them,
it is necessary that they should be compared together \d\\\ attention. P. centralis, which
may be considered as the type of this small generic group, differs from P. Gravesiana,
P. elongata, P. cylindrica, and P. MantelUi, by its costse being always straight, rather
thick and never sub-lamellous, and rather flexuous, as in the four last-mentioned species ;
it
is
also to be remarked, that its costae are rather more prominent near the basis than higher
up, whereas the contrary is seen in the P. Gravesiana, and that the loculi are never
subdivided by small dissepiments, as is the case in P. elongata, P. cylindrica, and
P. MantelUi. P. serpentina, which bears more resemblance to it, is characterised by the
septa forming only three cycla, and the costae being very delicate, and rather indistinct
towards the basis. But it is with P. Fittonii that P. centralis is most closely allied ; the
former, however, is of a thicker form, its tertiary costse are more developed and more
delicately granulated, and its columella is much larger, and terminated by a sub-papillose
surface.
The specimens of P. centralis which we had the opportunity of examining were found
in the Upper Chalk at Northfleet, near Gravesend, and at Norwich.
Mr. Phillips mentions
the existence of the same fossil at Dane's Dike;^ and Dr. Mantell has met with it at
Brighton, Lewes/ Steyning, and Heytesbury.* Mr. Graves also alludes to it as being
found in the Challc Formation of the Parisian basin at Beauvais / but we have much reason
to think that the species observed by that geologist is not the one here described, and must
be referred to our P. Gravesiana. M. Roemer and other authors equally apply the name
of C. centralis^ to
a fossil found in the north-west of Germany, but we have not been able
as yet to verify the propriety of this determination, not having seen any of the specimens
discovered in that part of the Continent.
^ The species described in that work under the names of Parasmilia pocuhim, P. Faitjasii, and
P. punctata, must now be referred to our genus Coelosmilia, which is characterised by the entire absence of
the cohimella.
- Op. cit., parti, p. 119. ^ lUygt^ ^f tj^g Geol. of Sussex, p. ICO.
* Geol. Trans., 2d series, vol. iii, p. 204, ^ Geogn. de I'Oise, p. 701.
8 Versteinerungen des Norddeutschen Kreidebirges, p. 26.