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 coste, 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 costa, 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 aline. The wall is very thm. ‘The cadice 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 granulated. The sepfa are thin and very exsert, but not quite so much 
so asin the Zurbinolia Dixonii;’ 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 are 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 mner 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 m 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 Turbinolide, published about a year ago, six 
species were described, and we now know double that number of true Turbinolic, 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,> by the 
number of the septa which in these two last-mentioned species form four cycla. An 
additional cyclum of cost distinguishes Zurdinolia Fredericiana* from it ; in Turbinolia 
Prestwichii, T. minor, and 7. firma,’ the cost are not so thin, prominent, and wide apart 
as in this species, and the last of these characters separates it also from Zurdinolia pharetra® 
’ See plate ii, fig. 1. 2 Michelin, Icon., pl. xliii, fig. 5. 
’ These species, as well as the others only quoted here, have been described at full length in our 
Monograph of Turbinolidee, published in the Annales des Sciences Naturelles, 3"° série, vol. ix. 
4 See pl. iii, fig. 2. ® See tab. iii, fig. 5. ® See tab. ii, fig. 5. 
7 See tab. ii, fig. 4. Contrib. to Geol., tab. vi, fig. 210. 
