16 BRITISH FOSSIL CORALS. 



occupy a line in length. No rudiments of a fourth cyclum of costas, and a well-marked 

 depression in calicular edge of the wall, corresponding to each of the intercostal spaces. 

 Calice with a very narrow, but rather deep fossula. Columella compressed, arched at the 

 apex, granulated on the surface, reaching in general to the same height as the septa, or 

 even higher, and presenting, in the part where it begins to become isolated, six vertical 

 striae, which are in continuity with the inner edge of the six primary septa ; rather lower 

 down, the columella is slightly contracted, and a vertical section of the corallum (fig. \b) 

 shows that its tissue is compact, and that towards the bottom of the visceral chamber it 

 becomes united with the septa, so as to form a solid mass. Septa thin, unequal, very 

 exsert, having their upper edge strongly arched near the outer margin, but concave near 

 the centre of the calice, slightly granulated laterally, and forming three cycla ; those of the 

 first and the second cycla nearly of the same height, but the secondary ones much broader 

 at the apex than the primary ones, and not extending so far up the columella. The 

 tertiary septa much narrower and shorter than the older ones ; very thin towards their 

 inner edge, and cemented to the primary septa, as in the preceding species (fig. lb). 

 Interseptal loculi large. Height of the corallum about four lines. Diameter of the calice, 

 two lines and one third. The form and the proportions not differing in the young and 

 in the adult specimens. 



Turbinolia Dixonii is the largest known species of the genus, but T. dispar and 

 T. Prcstwic/tii are almost of the same size. This species is very closely allied to T. sulcata, 

 from which it differs principally by its form (rather more inflated near the calice), by its 

 compressed columella, by its septa being more exsert, and its costse more projecting and 

 more distant. The breadth of the intercostal furrows distinguishes both T. Dixonii and 

 T. sulcata from T. Prestioichii, T. minor, T. firma, T. pkaretra, T. Nystiana, and 

 T. Bowerbankii. The existence of only three cycla of costal does not allow of its being 

 confounded with T. Fredericiana, T. dispar, and T. costata, and, finally, T. humilis is 

 easily distinguished from it by its cylindroid form, non-compressed columella, and 

 glabrous septa. 



Turbinolia Dixonii is a fossil very abundant in the London Clay at Bracklesham Bay, 

 and has probably been confounded with T. sulcata by Mr. Fleming, and some other 

 geologists, who mention the latter as being found in that locality, where it appears to be 

 very rare. In Mr. Dixon's work, now passing through the press, Mr. Lonsdale has also 

 described it as a variety of the T. sidcata of Lamarck. 



The specimens, the examination of which has enabled us to recognise this new species, 

 were given to us by Mr. Dixon and by Mr. Frederick Edwards. 



3. Turbinolia Bowerbankii. Tab. II, figs. 3, 3 a, 3 b. 



Corallum almost conical, rather short. Costa not very prominent ; those of the first 

 two cycla inflated near the basis ; the tertiary ones beginning at less than a quarter of the 

 distance from the basis to the calicular edge of the wall ; slight rudiments of a fourth 



