54 BRITISH FOSSIL CORALS 



The cyclical arrangement cannot be determined by the number of the septa ; there 

 are between four and five cycles. The largest septa reach the floor of the caHce, where 

 they join. 



The endotheca is greatly developed, and it forms small dissepiments, and others which 

 stretch across the corallites almost like tabulae. 



The marginal gemmation is frequent. 



Length of the largest calice '. inch. Depth i — ^ inch. 



Locality. Lyme Regis. 



In the Collection of R. Tomes, Esq. 



2. IsASTRiEA iNSiGNis, DuTican. PI. XIII, figs. 10, 11. 



The corallum is massive and forms a flat mass. The corallites are very equal in size 

 and regular in shape. 



The calices are placed very regularly in linear series ; they are shallow, open, and are 

 separated by a stout wall. The calices are generally hexagonal, but many are square. 



The septa are small, project but slightly from the wall, are dentate and unequal. 

 There are four cycles of septa in six systems in the largest calices. The primary and 

 secondary septa are nearly equal ; the tertiary are decidedly smaller, and the rest are 

 the smallest. 



The endotheca is close. 



There is no columella. 



Diameter of largest calices ^ths inch, and of the usual size j'bths inch. 



Locality. Lyme Regis. 



In the Collection of R. Tomes, Esq. 



This is a very well-marked species, and belongs to a section which comprises Isastraa 

 Hemcquei, Ed. and H., from the Lower Lias of Hettange, Isastraa polygonalis, MicheUn, 

 sp., of the Muschelkalk, and Isastraa Lonsdalei, Ed. and H., of the British Inferior Oolite. 



3. IsASTR^A Stricklandi, Dutican. PI. XIII, figs. 1 — 4. 



The corallum is very tall, has a small base, and is expanded superiorly. 



The corallites are unequal in size and length, and vary much in shape. 



The calices are very irregular in form and depth ; their walls are thick, and the septa 

 stout and very dentate. The dentations are blunted and are very large, and more so 

 internally than near to the calicular margin. 



The septal number varies, and 32 — 40 appear to be the usual number. The laminas 

 are stout, and the primary and secondary septa reach downwards to the base of the fossa 

 and are dentate. The others, which are short, are also stout. 



