69 



CHAPTER IV. =^ 

 PALEOZOIC CORALS AND FORAMINIFERA. 



ZOOANTHAIIIA. 



Petraia-\ gigas (M*^Coy). 



Sp. Char. Obtusely conical, slightly oblique, section elliptical; 

 internal cast divided into forty broad, flat, smooth ribs, sepa- 

 rated by the strong sulci of the principal lamellae reaching to 

 the centre ; each of those ribs is divided by a fine mesial sulcus, 

 the remains of the intermediate lamellse, not reaching to the 

 centre, making the total number of lamellse about eighty. 

 Length of imperfect cast 2 inches 7 lines ; width of long axis 

 at base 11 lines, at edge of cup 3 inches 7 lines (compressed), 

 width of ribs 2 lines. 



This large and strongly marked species from the number of 

 its lamellse can only be confounded with the P. pluriradialis 

 (Phil, sp.) and P. elongata (Phil, sp.), from both of which it dif- 

 fers in its form and great size, width of ribs on the cast, absence 

 of the punctures, &c. The strong primary lamellse reach the 

 centre with a very slight indication of twisting ; the secondary 

 ones are very delicate towards the base, but become nearly equal 

 in strength to the others as they approach the edge of the cup. 

 The denticulation of the lamellse is scarcely perceptible. 



Not uncommon in the fine gray Devonian slates of New Quay. 



{Col. University of Cambridge.) 



* The descriptions in this chapter date from the ' Annals of Natural 

 History ' for January and February 1849. 



f Having examined Count Miinster's original specimens of several spe- 

 cies of his genus Petraia, I have satisfied myself that they are really corals, 

 as suggested by Mr. Lonsdale and others, although he describes them in his 

 ' Beitrage ' as Gasteropods, the publication of which view prevented Prof. 

 Phillips adopting the genus in his work on the Fossils of Devon and Corn- 

 wall. 



