CORALS FROM THE INFERIOR OOLITE. 139 



3. ISASTREA LONSDALII. 



All the specimens of this species which we have seen were in so bad a state of preser- 

 vation, that we did not consider them worthy of being figured in this Monograph. The 

 calices are not very unequal in size, and rather shallow; the septa are thin, straight, and 

 form four cycla ; those of the first two cycla differ but little in size ; the last cyclum is 

 more or less incomplete ; great diagonal of the calices two lines and a half. 



This fossil was found in the Inferior Oolite at the foot of Lansdown, near Bath, and 

 was given to the Geological Society of London by Mr. Pratt. 



Some casts found in the Inferior Oolite at Charlcomb and at Dundry, appear to belong 

 to corals of this genus ; they show very unequally developed prismatic calices, but cannot 

 be characterised specifically. 



Genus Thamnastrea, (p. xliii.) 

 1. Thamnastrea Deeranciana. Tab. XXIX, figs. 3, 3a, 33; and 4, 4«, 4/5. 



AsTREA Defranciana, Micheliu, Icon. Zooph., p. 9, tab. ii, fig. 1, 1840. 

 Synastrea Defranciana, Milne Edwards and J. Haime, Ann. des Sc. Nat., s. 3, vol. xii, 



p. 1.53, 1849. 

 — — B'Orbigny, Prod, de Paleont., tab. i, p. 292, 1850. 



Thamnastrea Defranciana, Milne Edwards and J. Haime, Polyp, des Terr. Palaeoz,, &c., 

 p. no, 1851. 



Corallum in general thin, discoid or somewhat turbinate ; its common basal plate 

 covered with a complete epitheca strongly wrinkled ; its upper surface almost flat, in some 

 slightly convex, in others concave. Calices superficial, arranged in concentric lines, rather 

 irregular, and having a very small central fossula. Columella quite rudimentary. Septa 

 very closely set, very thin, rather flexuous, and in general more developed in the direction 

 of the radii of the compound corallum, than in the opposite direction, completely confluent, 

 and presenting very closely set, regular crenulations at their upper edge. In general they 

 form three complete cycla ; but in some individuals the third cyclum is rather incomplete, 

 and in others rudiments of a fomih cyclum appear in some of the systems. Breadth of the 

 caHces one line and a half. 



When the calices are worn down, the polygonal walls become very distinct (fig. 33), 

 and this coral then assumes an appearance very similar to that of a fossil, much weather- 

 worn, that was found at Dundry by our friend Mr. Bowerbank, and is figured in our 

 XXIXth Plate under the number 4 ; the size of the calices is not quite the same, and we 



