LOWER CARBONIFEEOUS FOSSILS. 511 



MENOPHYLLUM Milne Edwards and Haime, 1850. 



MENOPHYLLUM (?) EXCAVATUM 11. Sp. 

 PI. LXVII, figs, la, lb, lc, Id, le, If. 



Corallum simple, regularly and rather rapidly expanding, very slightly 

 curved. Length of an average specimen, 41 mm.; diameter at the top, 

 23 mm. Septa of two series. Calyce very deep, half or more than half 

 the entire length of the corallum. In the calyce the primary septa are short 

 and the secondary septa shorter still. . Below, only the primaiy septa are 

 well developed. They are there sometimes so thickened by stereoplasma 

 as to make the bottom of the corallum almost solid. There is no columella 

 nor dissepimental development, but a well-marked fossula is always present. 



The deep calyce uninterrupted by transverse partitions, the smaller 

 number of septa, and large fossula, strongly characterize this form 



There is only one species of Menophyllum known heretofore, M. tenui- 

 marginatum; and M. excavatum is, so far as I am aware, the first reference made 

 to the genus in this country. This reference may, however, perhaps justly 

 be called in question, since M. tenuimarginatum is said to possess crescent- 

 shaped tabulae, and to be allied to Amplexus, while M excavatum is without 

 tabula? and dissepimental tissue. On the other hand, as seen in transverse 

 sections, the structure of the two forms seems to be so closely analogous 

 that I can not but believe that, if not congeneric, M. excavatum is at least 

 nearly allied to M. tenuimarginatwn. It resembles the genus Cyathaxonia 

 in being without tabula? or dissepiments, but differs from it in lacking a 

 columella as well. I have avoided the genus Petraia, which is perhaps 

 founded on a similar type, for it is little known and can scarcely be regarded 

 as well established. Nor do I believe a reference to Zaphrentis to be war- 

 ranted, for, as before stated, M. excavatum is without endothecal structure 

 except the septa, and the manner in which the ends of all the septa are bent to 

 form an inclosing wall for the fossula is very characteristic, 



Compared with M. tenuimarginatum, M. excavatum has fewer primaiy 

 septa, and those of the second order are not so well developed. 



The structures of the earlier corallum of this coral have not been 

 observed. The secondary septa attain only an inconsiderable development. 

 There are about twenty-six primary septa, which are bent at the ends and so 

 united as to leave a large fossula, reaching to the center of the theca. The 



