138 BRITISH FOSSIL CORALS. 



Genus Isastrea. 



1. Isastrea Richarusoni. Tab. XXIX, figs. \, \ a. 



Corallum massive, flat, or slightly gibbose. Calices polygonal, very unequal in size, 

 shallow, and separated by a strong single wall. Fossula distinct ; no appearance of a 

 columella. Septa rather thin, often somewhat curved, unequal in size, and forming three 

 cycla ; in one or two of the systems, those of the last cyclum are sometimes deficient, and 

 in other cases a few septa belonging to a fourth cyclum are seen; in general, the six 

 primary ones are much larger than the others, and become thicker near their inner edge, 

 but sometimes the secondary ones are almost as much developed in one of the systems. 

 Diameter of the calices in general one line and a half, the large ones two lines. 



This fossil was found in the Inferior Oolite at Dundry, by the Rev. B. Richardson, and 

 presented by that gentleman to the cabinet of the Geological Society of London. We are 

 inclined to refer to the same species a coral found at Beachencliff by Mr. Walton. 



By its general aspect Isastrea RicJiardsoni resembles /. limitata^ and /. explanulataf but 

 it may be easily distinguished from them as well as from most species of the same genus, 

 by the thickness of the principal septa near their inner edge ; this character is also met 

 with in I. Munsterana,^ but in the latter the calices are much larger, and the septa are 

 more numerous and closer set. 



2. Isastrea tenuistriata. Tab. XXX, figs. 1, la. 



AsTREA TENUISTRIATA, M'Coij, Ann. and Mag. of Nat. Hist., s. 2, vol. ii, p. 400, 1848. 



Corallum massive, terminated by an almost flat surface. Calices not very unequal in 

 size, and shallow. Walls not well developed. Septa, about seventy-two in number, thin, 

 closely set, straight, or slightly curved, and rather unequal in size from foiu" to four, or 

 especially alternately \ dissepiments rather closely set. Breadth of the calice half an inch 

 or more ; depth one line. 



The specimen here described was kindly communicated to us by Dr. Wright, of 

 Cheltenham, and was found by that naturahst in the Inferior Oolite at Crickley ; there is 

 another specimen from Dundry in the Cambridge Museum. 



/. tenuistriata difters from all the other species of the same genus by the great number 

 of its septa. 



1 Tab. xxiv, figs. 4, 9. ^ Tab. xxiv, fig. 3. 



3 Prionastrea Munsterana, Milne Edwards and J. Haime, Ann. des Sc. Nat., s. 3, vol. xii, p. 136. 



