CORALS OP THE LONDON CLAY. 19 



up, if they had corresponded to septa belonging to the third cycluoi. All the septa are 

 veiy thin, almost glabrous, exsert, and terminated by a regularly arched apex, rising more 

 or less, according to the cyclum to which they belong. Height not quite a line and a half; 

 diameter of the calice two thirds of a line. 



This Coral is one of the smallest of the genus Turbinolia, and is indeed usually even 

 smaller than the species designated by the name of Turbinolia minor, for which it may very 

 easily be mistaken ; its characteristic features can only be seen with the help of a lens, 

 but when sufficiently 'xiagnified, the appearance of its walls will make it immediately 

 recognisable ; for in T. minor the costae are very thick, crenulated lateraEy, and the inter- 

 costal furrows do not present any dimples, whereas in T. humilis the^e dimples are well 

 marked, and the costae are thin. These two species are the only ones of the genus that 

 have apparently but five tertiary systems, and their diminutive size contributes also to 

 make them not easily recognisable. 



Turbinolia humilis is found in the London Clay at Barton, where it appears to be 

 abundant. We are indebted to Mr. F. Dixon and Mr. Frederick Edwards for the 

 specimens in our possession. 



6. Turbinolia minor. Tab. II, figs. 5, 5 a, 5 b. 



Turbinolia minor, Milne Edwards and J. Haime, Annales des Sc. Nat., 3 me serie, vol. ix, 

 p. 239, 1848. 



Corallum of a cylindrico-conical form, rather short, and very obtuse at its basis. Costa 

 very thick, closely set, and not very prominent ; those of the first and second order par- 

 ticularly thick near the basis ; the outer edge of all very obtuse, and their sides delicately 

 crenulated. Intercostal furrows very narrow, linear, and presenting no trace of the dimples, 

 which are so apparent in the preceding species. The form of the costae is particularly well 

 marked near the calice (fig. 5 b), the lateral crenations of which are sometimes so developed 

 near the basis, that they assume a crispate appearance ; in other specimens they are scarcely 

 visible, but the variations met with in the form of these parts are never such as to make 

 them resemble the costae of T. humilis. Calice very deep. Columella cylindrical, slender, 

 and exsert, Septa belonging to three cycla, and appearing to form only five systems, 

 although there are in reality six systems as usual ; only in two of these there are no 

 tertiary septa, and the secondary septa are of the size of the other tertiary ones, but 

 correspond to secondary costae, the development of which are normal (fig. 5 b). All the 

 septa are thin, exsert, and slightly granulated on their lateral surfaces ; the secondary ones 

 are nearly as large as those of the first order, but those of the third cyclum are much 

 smaller. This species is always remarkably small ; it is not more than a line and a half 

 high, and two thirds of a line in diameter. 



