558 R. F. TOMES ON MADREPORAR1A EROM THE CORAL RAO 



appearance of a common wall or epitheca. The calices are large, 

 rudely hexagonal, and internally united by their walls, which are 

 thin but distinct. The columella is about one fourth of the diameter 

 of the calice ; it is stylif orm and prominent. The septa are rather 

 thin, straight, and the primaries and secondaries run into the 

 columella. Those of the third cycle are two thirds the length of 

 the first and second, and those of the fourth are half the length of 

 the third. There is a tendency in the short septa to incline 

 towards or run into the longer ones. All have their sides marked 

 with vertical ridges, which terminate in their margins, and form 

 papillae which have their greatest diameter across the septa. In 

 almost every instance those of one calice meet and blend with those 

 of other calices at the upper margin of the wall, as in Clausastrcea. 

 The dissepiments are numerous, thin, and affect a somewhat cir- 

 cular disposition when seen directly from above. In form they 

 are rather like synapticulge, from which, however, they are quite 

 distinct. 



Increase takes place in this species by gemmation on the walls 

 between the calices, just as in Isastrcea. 



The diameter of the calices is about three lines, but sometimes as 

 much as four or four and a half lines. 



It occurs, and is not rare, in the Coral Eag at Headington, near 

 Oxford, at Lyneham, Wiltshire, at High worth, and at Marcham, from 

 all which places I have obtained specimens. 



Family FUNGIDJS. 

 Genus Thamnastr^a, Le Sauvage. 



Thamnastr^a arachnoides, Edw. and Haime, Pol. Toss, des Terr. 

 Paleoz. p. Ill, 1851 ; Brit. Foss. Cor. p. 97, 1851. 



Synastrcea aracJmoides, Edw. and Haime, Ann. des Sci. Nat. 

 3 e ser. t. xii. p. 154, 1850. 



Of this well-known species I have lately made an exhaustive 

 examination, with a view to determine, if possible, whether it is a 

 perforate or imperforate Coral, and I am now fully convinced that 

 the septa are strictly imperforate. This will render it necessary 

 that it should be removed from such of the Tliamnastrceoe as have 

 been shown by Milaschewitch to appertain to the Poritidae *. 



It is probable that the Middle-Lias species, which I have described 

 under the names of Thamnastrcea Mheridgii, and T. Walfordi f, 

 as well as T. Criclcleyensis and T. Duncani J, from the Inferior 

 Oolite, have imperforate laminae. These, with perhaps also Tham- 

 nastrcea Manseli of Prof. Duncan § and some others, will most 

 likely be found to constitute a distinct genus ; for whether we 



* Palasontographica, vol. xxi. 



t Quart. Journ. Geol. Soc. vol. xxxiv. p. 179, and vol. xxxviii. p. 95. 



\ Ibid. vol. xxxviii. pp. 435 and 436. 



§ Suppl. Brit. Foss. Cor. pt. iii. p. 20. 



