CORALS FROM THE CORAL RAG. 75' 



The corallites arc very tall, aiul the caliccs vary somewhat in size in the different 

 specimens A\'hich have come under our observation ; in small adult individuals their 

 vi'idth (at the great diagonal) is about two and a half lines, and in the large ones scarcely 

 more than three lines. 



The genus Isastrea comprises a considerable number of species, the list of which has 

 been given in our above-mentioned work. Li order to avoid unnecessary details, we will 

 therefore only add, that T. ohlonga is easily distinguished from the other British fossils 

 belonging to the same generical group, by the thickness of its walls, and the strong lateral 

 granulations of the sejda. By its general aspect this coral bears some likeness to the 

 Isastrea polycjonalis} a fossil of the Muschelkalk, of which the cast only has as yet been 

 found ; but in this last-mentioned species all the scj)ta of the fourth cyclum are well 

 developed. 



Isastrea oMonga has been met with only at Tisbury, Wiltshire. The specimens which 

 we have examined belong to the collections of the Geological Society of London, the 

 Museum of Bristol, the Museum of Paris, Mr. Bowerbank, and Mr. Stokes. 



CHAPTER IX. 



CORALS FROM THE CORAL RAG. 



The Coral Rag, as may be inferred from its name, is a deposit most abundant in fossil 

 corals ; but the number of species found in this Formation is by no means proportionate to 

 that of the specimens met with. The British species are indeed very limited ; and, although 

 we have had access to all the richest palaeontological collections in England, we have only 

 seen fourteen species of true corals belonging to this portion of the oolitic series. Tw^elve 

 of these are Astreidce, and two Fungida ; five of these species are also found in the Coral 

 Rag of France and Germany ; the nine others are, as yet, peculiar to England. One 

 {Thamnastrea concinna) appears to exist also in the Great Oolite, and probably even in the 

 Inferior Oolite; but most have not lieen met with in any other Formation. 



The principal fossiliferous beds, from which these corals have been obtained, are 

 situated at Steeple Ashton, in Wiltshire, and Malton, in Yorkshire. Some species have 

 also been found at Hackness, in Oxfordshire ; at Osmiugton, near Weymouth ; at Upware, 

 in Cambridgeshire, &c. 



1 Asfrea' polygonal is, Michelin, Iconogr., lab. iii, fig. 1. • 



