76 A. E. Yerrill — Bermudian and West Indian Reef Corals. 



septa are alternately thicker and thinner, and show numerous lateral 

 spinules, as mentioned above. See pi. x, fig, 4. 



This species can usually be easily recognized by its evenly convex 

 surface and the long convoluted simple, often gothic ridges, with 

 the crest of the wall, thin, solid, and often in a zigzag line ; by its 

 rather open grooves, generally wider than the ridges, and usually 

 showing rather oj^en interseptal spaces and thin unequal septa ; and 

 especially by the strongly spinulose lateral surfaces of the septa. 



The width and depth of the actinal grooves varies considei-ably, 

 but is almost always greater than in lahyrinthiformis. The breadth 

 from wall to wall is generally 8 to 14"""^ rarely as little as 6""" ; open 

 space between septal edges, near summit, mostly 6 to lO"""" ; depth of 

 grooves mostly 6 to 10"'™, usually about 8'"™. Number of septa to a 

 centimeter, usually about 24 to 28, when the smaller ones are 

 developed. 



The color of this species, in life, so far as observed by me at the 

 Bermudas, is dull yellow, ocher-yellow, or brownish yellow. It 

 appears not to have the orange-yellow color, so general in l(ib)/rrnth- 

 iformis. In the Bahamas it is more variable in color. 



I think it very improbable that all the various color-varieties, 

 named by Lesueur from the color alone, pertain to this species. 

 But in any case they cannot be determined from color alone, for the 

 color of such corals is variable and uncertain. Therefore M. viridis 

 of Lesueur rests on no valid characters. 



This species is not abundant in the Bermudas. It is sometimes, 

 though rather rarely, found on the inner reefs, associated with the 

 preceding species, but it occurs more commonly on the extreme 

 outer reefs. Most of the larger specimens that I have seen were 

 from the vicinity of the North Rocks, where it becomes one to two 

 feet or more in diameter. It is common in the West Indies and on 

 the Florida Reefs, where it grows to a large size. I have seen 

 specimens over a yard across. 



At least two forms of simple ridged Mwandrce occur on the outer 

 reefs of the Bermudas. Whether they represent more than varieties 

 of the above species may be doubtful, for no one has yet obtained a 

 sufficiently large series of them for study. Those that I have seen 

 appear to me to belong to two species, for they differ decidedly as 

 to the form and denticulation of the septa and in other ways. The 

 more common form seems to be the abundant West Indian and 

 Florida species, named above, 



I am not prepared to admit that all the described West Indian 



