92 THE VOYAGE OF H.M.S. CHALLENGER. 
of which it may prove to be simply a very thick and hard triangular-walled variety. At 
the outer part of the corallum the ridges are. rounded and much damaged. 
Locality.—Bermuda. 
3. Mexandrina strigosa, Dana. 
Meandrina strigosa, Dana, Zoophytes, p. 257, pl. xiv. fig. 4. 
A most interesting series of twenty-nine specimens of this species was obtained. 
They are of all sizes from about 10 cm. in diameter to more than 30 cm., the largest 
being about 18 em. high. They are either hemispherical, subglobose or broadly convex, 
oblong or reniform—the hemispherical being the prevailing form. The species is subject 
to very great variation, and there are at least three forms which, in the absence of the 
other intermediate ones, might have been considered distinct. Pourtalés has already 
pointed out this variability as seen in two of the Florida forms; one with rather narrow 
gyri, thin walls, paliform lobes distinct but not very prominent ; the other with wider gyri, 
wall rather thick, sometimes flattened and slightly furrowed on the top, and paliform 
lobes very distinct. This second form had previously been referred by Verrill to Mzan- 
drina sinuosa, Lesueur. 
While it is possible to select five or six specimens from the series as being more or 
less distinct, it is advisable to remark that the characters by which they may be dis- 
tinguished are extremely variable, as shown by other specimens, and even by the 
same specimen at the outer part of the corallum. The following five forms may be 
described in order to bring more prominently forward the great modification which the 
species may undergo :— 
a. Gyri very deep, about 7°5 mm., with a width of from 6 to 8 mm.; walls thick; 
septa with free border vertical, paliform lobes very distinct, rather thick ; 
width of ridges above the paliform lobes from about 4 to 5 mm.; columella 
very abundant, forming a continuous mass about 2°5 mm. wide. 
b. Gyri very deep, about 7 mm., with a width of 6 mm.; walls very thin; septa 
with free border vertical, paliform lobes very distinct and thin; width of 
ridges above the paliform lobes about 3 mm.; columella very abundant, 
forming a continuous mass about 2°5 mm. wide. 
c. Gyri rather deep, from about 5 to 6 mm., with a width of from 4 to 5 mm.; 
walls very thin; septa with free border vertical, paliform lobes very distinct, 
those of opposite sides almost meeting and hiding the columella, so as to give 
a shallow appearance to the valleys, but often widening out at very close 
distances for the calicinal centres, which at the sharp curves of the ridges are 
quite distinct; width of ridges above the paliform lobes about 3 mm., 
columella abundant, almost hidden by the paliform lobes. 
