CORALS OF THE LONDON CLAY. 27 
has induced us to think that each group composed of three lamin, and corresponding to 
one costa must be the homologue of a single normal septum. It also appears evident 
that the first-mentioned hypothesis is incompatible with the mode of development of the 
younger septa corresponding to the short costa ; for wherever one of these younger coste 
interposes itself between two older ones, a new group of three septal laminze makes its 
appearance in the visceral chamber, between two of the old lateral plates, which, according 
to this view, would belong to one septum, and a young septum, accompanied by two 
half septa, would thus be included m the mterior of an elder septum. Nothing of 
the sort is ever met with in any known corallum, and would be contrary to the general 
laws which appear to regulate the formation of the septal apparatus; but if we admit that 
each group of these vertical lamin corresponds to a single septum in the ordinary 
Polypidoms, all serious difficulties disappear, and a circumstance that tends to corroborate 
this view of the subject, is, that im some Turbinolide an intermediate tissue is seen between 
the two lateral plates constituting each of the larger septa, so that if these three vertical 
strata of sclerenchyma, instead of bemg in contact, and intimately united, were separated 
by a membranous fold or duct, each septum would no longer have the appearance of a 
simple partition, but would resemble the trilamimate septal groups of the Dasmia. In the 
present state of our knowledge concerning the structure and the mode of development of 
this curious fossil, we must be cautious in our speculations concerning the signification of 
the parts just described; but it is to be hoped that a complete solution of the question 
will be obtained by the study of a greater number of these Corals. At all events, the 
development of the septal apparatus must be very abnormal in Dasmia, and appears to 
warrant the establishment of a separate zoological division for the reception of this extinct 
genus. 
Family OCULINIDAI (p. xix). 
1. Genus OcuLINA (p. XIX). 
Ocurina conrerta. Tab. II, figs. 2, 2a, 24. 
Corallum composite, incrusting, forming an irregular, subglobose, or lobated mass, and 
appearing to have always grown on some extraneous stem, which has disappeared during 
the process of fossilization. The corallites are not arranged in a regular way, but are 
usually very closely set, and the calices are unequally prominent on the surface of the 
coenenchyma, which is compact, and moderately thick ; its surface is covered with round, 
unequal, crowded granulations, and presents no distinct costee. The ea/ices are in general 
quite circular, excepting when preparmg to multiply by fissiparity, which is very seldom 
the case; the edge is rather thin, and the fossula large, but not very deep. The columella 
is sub-papillose. The septa (fig. 24) constitute three complete cycla, besides which some 
