226 A. E. Verrili—The Bermuda Islands; Coral Reefs. 
even a question whether these two be really distinct species in the 
broader sense, for they nearly intergrade, or else hybridize more or 
less. 
The chief differences are in the closer and thicker radial septa, 
their fewer, shorter and stouter, often triangular or saw-tooth shaped 
denticulations, and other details of structure. 
The type of Symphyllia knoxi Duch. and Mich., of which Dr. 
Vaughan has sent me a photograph,,is a young dipsacea, very much 
like my figure 2, pl. xix, these Trans., vol. xi. It consists of six 
broad, shallow, mature calicles grouped around a primary simple 
S43 er Senna 
Figure 79.—Mussa dipsacea. About 3} nat. size. Phot. by A. H. V. 
one; some of them are nearly circular and simple ; others are 
becoming lobed. The septa are numerous, close together, not very 
unequal; the teeth are strong, triangular, and rather regular. 
The remarkable and elaborate figures drawn and lithographed by 
Mr. A. Sonrel for Prof. Louis Agassiz, but eventually published by 
A. Agassiz, with explanations by Pourtalés (Florida Reefs, pl. vu, 
figs. 1-8), are perhaps as accurate as can be made by lithography. 
But such corals cannot be satisfactorily represented except by pho- 
tography. Pourtalés referred them all to dipsacea, but he was at that 
time unacquainted with the type of fragilis. They all have slender 
crowded teeth and appear to me to belong mostly to fragilis. Fig. 
