DIPLOHELIA. 23 



Oculina disticha were fragments of the younger branches of Oculina 

 varicom Les. They were obtained 



Oir Condi Reef, in 40 fathoms. 

 Oil' American Shoal, In 43 fathoms. 

 Off" French Reef, in ."iO fathoms. 



The description and figure of L&sueur are so imjaerfect, that they 

 may ajiply to almost any species of the genus. Dana's descrij^tion, 

 however, really establishes the species, and is prior to Milne-Edwards 

 and Hainie's, who evidently referred to the same object. Why they 

 should make Dana's species a synonyme of 0. diff'um is not very 

 clear. 



Oculina tenella Pourt. 

 Plate v., figs. 11 and 12. 



Corallum branching irregularly, slender. Ca^nenchyma finely gran- 

 ulated. Costse distinct only on the border of the calicles, which are 

 circular, irregularly alternate, very prouunent, about one diameter 

 apart, and as wide or slightly wider than the branches. Fossa mod- 

 erately deep. Septa finely serrated, slightly exsert in six systems 

 and three cycles. Pali before the primary and secondary septa. Colu- 

 mella papillose, more deeply sunk than the pali. 



Smaller branches about 2 mm. in diameter. Calicles 2 to 2.5 mm. 



Off Tortugas, in 3G fathoms. 



Oculina diffusa Lajik. 

 Was obtained living as deep as 15 fathoms. 



DTPLOHELTA M.-Edw. & II. 



Attention has lately been drawn by Dr. Duncan to the difficulty of 

 distinguishing from each other the genera Diplo^iielia, Amphihelia, and 

 Lophohelia of Milne-Edwards and Haiuie. Like others of the genera 

 established by these authors and based on very few species, they 

 become very perplexing as our collections increase and the distinc- 

 tive characters are found not to be so precise as they were at 

 first enounced. My opportunities for the study of this giTJU]) have 



