76 ORBICELLA 



ASTR^JACE^ M.-Edw. & H. 

 ORBICELLA Dana. 



Heliaslrcea M.-Edw. & II. Hist. Nat. des Corall. 



Axinni M.-Edw. & II. Compt. rend, de l'Acad. des Se. 1848, and Ann. des Sc. Nat., 3' Se>., t. XI. 



The name adopted by Dana covers so nearly the same ground as 

 the generic division called Heliastnea by Milne-Edwards and Haime, 

 that it is retained here, as had already been done by Mr. Verrill in the 

 Bull. Mus. Comp. Zool., No. 3. 



Orbicella cavernosa VerrIli.. 



Madrepi Ellis. (Astrcea, Heliaslrcea, Orbicella radiata Auct.) 



Madrepora cavernosa Ksper, Pflanz. Suppl., p 18, PI. 37.* 



Astrea argus Lamk. 



Tubaslrea cavernosa Blaixv. 



Orbicella argus I 'ana. 



Astrea cavernosa M.-Edw. & II. Ann. des Sc. Nat, 3« Ser., t. XI. 



Heliaslrcea cavernosa M.-Edw. & II. Hist. Nat. des Corall. 



Heliaslrcea conft Ha M.-Edw. & II. 



There is considerable variation among the specimens from Florida in 

 the Mus. Comp. Zool., enough apparently to warrant placing them 

 among the three species named in the synonymy ; but by carefully 

 examining the different parts of each specimen, passages from one to 

 the other can be found. Thus young polypidoms, expanding rapidly 

 laterally, and with rather distant polyps, appear at first to differ con- 

 siderably from strongly convex ones with crowded calicles ; the costse 

 are longer. Hatter, and less sharply denticulate, and the border of the 

 calicles less elevated. 



The size of the calicles. relied on to divide the genus into groups, by 

 Milne-Edwards and Haime. is a very uncertain character ; one specimen 

 has in one part the calicles varying from 3.5 to 4.5 mm., in another part 

 from 7 to 8 mm. The same specimen has in some parts the contiguous 

 walls united solidly, with very lew or no exothecal cells, in others sep- 

 arated by an abundant cellular exotheca. In worn specimens the last 

 cycle disappears first, for that reason probably Orbicella (Madrcjiora) 

 radiata Ellis has been characterized by Milne-Edwards and Haime as 

 having but three cycles. 



This coral is generally found from 2 to 15 fathoms deep, forming 

 sometimes masses of considerable size. It is also occasionally found in 

 smaller masses in lesser depths on the reef. 



* I have nut seen tins figure, the copy of fcper which I have consulted being incomplete. 



