420 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 6, 



lites crowded, cylindrical, distinct, very long. Costae snbequal, large ; 

 those of the fourth order sometimes wanting. Calices circular, 

 from -j^ to -^j inch in diameter. Septa very delicate, very crowded, 

 nearly linear, granular. Endotheca greatly developed, vesicular, 

 with from three to four dissepiments between the septa, dividing the 

 loculi into compartments. The fourth cycle of septa appears often 

 to reach one of these dissepiments, and to end by touching it. Colu- 

 mella well developed. 



From the lower part of the Marl-formation of Antigua. Coll. Geol. 

 Soc. 



This is a variety characterized by a larger amount of endotheca 

 and a smaller amount of exotheca than in the typical form. 



Yar. 2. 



A variety with the specific details of the typical form, and in ad- 

 dition an increased amount of exotheca, whose cells are broader than 

 high, the dissepiments being well developed. 



Prom the lower part of the Marl-formation of Antigua. Coll. Geol. 

 Soc. 



Yar. 3. 



A variety with smaller corallites, longer and more crowded deli- 

 cate septa, with the endotheca greatly developed, the dessepiments 

 being very stout. 



From the calcareous beds in the lower part of the Marl-formation 

 of Antigua. Coll. Geol. Soc. 



5. Astrjea megalaxoxa, spec. nov. PL XIII. figs. 12 a, 12 b. 



Corallum large. Corallites very numerous, crowded, very variable 

 in breadth, long and slender ; they have suffered much from mu- 

 tual pressure, and although the walls are distinct, yet the coral- 

 lites are often more or less polygonal ; diameter from g to -^ inch. 

 Walls thin. Costae small. Septa very delicate, a little thicker at the 

 wall than elsewhere, and very thin towards the columella ; in six 

 systems, the cycles varying greatly ; thus, in many corallites there 

 are two cycles, in others two cycles and a third in one or more 

 systems. Three perfect cycles are seen in large corallites, and two 

 additional septa in some (in the whole corallite). The primary septa 

 have a tooth near the wall; the secondary are a little smaller than 

 the primary. Columella lax, parietal, occupying a very large space. 



The details can be made out in only one corallite, which has 

 escaped the ruinous but remarkable fossilization that has destroyed 

 them in most of the specimens. The details have nearly all disap- 

 peared in the mass, and the interseptal loculi look like blunt, thick 

 septa. In some specimens the large space occupied by the colu- 

 mella is filled with silica of a white or of a black colour, giving them 

 a. very curious appearance. 



There are many corallites which appear to have been undergoing 

 fissiparous growth, but it is evident that extra-calicular gemmation 

 also occurred. There are few details left for a diagnosis of the spe- 

 cies. The recent Astrcea Pleiades, a Pacific form, is the only known 



