14 BRITISH FOSSIL CORALS. 



the adult state. The intercostal grooves are deep and broad ; near the calice a small 

 longitudinal line is visible in each of them, and indicates the existence of a fourth cyclum 

 of rudimentary costal, which do not correspond to any of the septa on the inner side of 

 the wall. These vertical furrows also present a double series of small dimples, which are 

 prolonged laterally on the sides of the costal, so as to constitute a sort of transverse fluting, 

 and are arranged alternately ; they are very closely set, and about fifteen occupy the space 

 of a line. The wall is very thin. The calice is circular, and its fossula is not very deep. 

 The columella is terminated by a conical, pointed apex, which rises higher than the septa, 

 and is delicately granulaied. The septa are thin and very exsert, but not quite so much 

 so as in the Turbinolia Bixonii -, 1 their upper edge is strongly arched, and their lateral 

 surfaces present small granulations, which form short submarginal, radiate lines near the 

 apex, and are arranged in nearly horizontal rows towards the lower part of the visceral 

 chamber. The inner edge of the apical portion of the septa is slightly concave, and soon 

 becomes horizontal, so as to meet the columella, to which it unites. A projecting line 

 extends from each of the six primary septa up the apical portion of the columella ; the 

 secondary septa join the columella much lower down, but they aie broader than the primary 

 ones. The tertiary septa are narrower at the apex, and less exsert than the preceding ones ; 

 they converge towards the intermediate primary septa, and become united to them all along 

 their inner edge, at about two thirds of the breadth of the latter. The height of the 

 corallum is usually about three or four lines, and the diameter of the calice about one line 

 and a half. In young specimens the calice is larger in proportion. 



This fossil is the only species belonging to the genus Turbinolia as now circumscribed, 

 which was known at the time when Lamarck first established the group bearing that name. 

 Shortly afterwards, Mr. Defrance discovered a second species, and Mr. Isaac Lea has since 

 then found a third. In our Monograph, of Turbinolidse, published about a year ago, six 

 species were described, and we now know double that number of true Turbinolise, but 

 they all belong to the same geological period, and are imbedded in Eocene deposits. They 

 appear to be more abundant in England than elsewhere ; the London Clay contains eight 

 species, only one of which (the fossil just described) has been met with in the synchronous 

 formation of the Parisian basin. 



Turbinolia sulcata differs from Turbinolia dispar, and from Turbinolia costata, 3 by the 

 number of the septa which in these two last-mentioned species form four cycla. An 

 additional cyclum of costae distinguishes Turbinolia Fredericiana 4, from it ; in Turbinolia 

 Prestwic/iii, 5 T minor, 6 and T.firma? the costse are not so thin, prominent, and wide apart 

 as in this species, and the last of these characters separates it also from Turbinolia p/iaretra* 



1 See plate iii, fig. 1. 2 Michelin, Icon., pi. xliii, fig. 5. 



3 These species, as well as the others only quoted here, have heen described at full length in our 

 Monograph of Turbinolidse, published in the Annales des Sciences Naturelles, 3 me serie, vol. ix. 



4 See pi. hi, fig. 2. 5 See tab. iii, fig. 5. 6 See tab. ii, fig. 5. 

 ? See tab. ii, tig. 4. Contrib. to Geol., tab. vi, fig. 210. 



