CORALS OF THE LONDON CLAY. 27 



has induced us to think that each group composed of three lamina?, 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 costae ; for wherever one of these younger costae 

 interposes itself between two older ones, a new group of three septal laminae 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 in the interior 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 laminae 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 in some Turbinolidae 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 being 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 trilaminate 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 OCULINID^ (p. xix). 



1. Genus Oculina (p. xix). 

 Oculina conferta. Tab. II, figs. 2, 2 a, 2 h. 



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 

 ccenenchyma, which is compact, and moderately thick ; its surface is covered with round, 

 unequal, crowded granulations, and presents no distinct costae. The calices are in general 

 quite circular, excepting when preparing 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. 2 b) constitute three complete cycla, besides which some 



