132 Prof. G. Lindstrém—On the Operculate Corals. 
ing to Lindstrém, to have been in error respecting the number of 
the septa in the coral. This species is characteristic of the Devonian, 
and has a wide distribution, having been found in the Hifel District 
(where it is exceedingly abundant), also in the Harz-mountains ; near 
Chimay in Belgium ; in Devonshire; Asturias in Spain, and in the 
Altai district. 
There are six species of Rhizophyllum, Lind.; four of which, viz. 
R. gotlandicum, F. Roemer, sp., 2. Gervillei, Bayle, sp., ER. tennes- 
seense, F. Roemer, sp., and R. australe, R. Etheridge, jun., are simple 
forms, whilst the other two species, Rf. elongatum, Lind., and R. af- 
tenuatum, Lyon, are compound forms; the former species increasing 
by calicinal budding, and the latter by stolons from the angles of the 
under-side of the calice. With the exception of &. Gervillet from 
the Lower Devonian of Néhou in France, the other species of the 
genus occur only in the Silurian of Gothland, New South Wales, the 
United States and China. 
The genus Platyphyllum, Lind., is distinguished from Rhizophyllum 
by its strongly-developed septa; the operculum was probably single. 
Only one species, P. sinense, Lind., is known from the Silurian of China. 
The genus Goniophyllum, Edw. and Haime, with its peculiar 
pyramidal form, has an opercular apparatus of four valves, two of 
which, viz. those of the under and upper sides of the calice, are 
trapezoidal in form, and constitute one pair, whilst the valves of the 
right and left sides are triangular, and constitute the other pair. 
The valve of the under-side is the largest, and probably the oldest of 
the four, and is the only one which is completely homologous with 
the operculum of Calceola and Rhizophyllum. Occasionally some of 
the opercular valves fall off, and are replaced by new valves. There 
are two species of the genus, G. pyramidale, Hisinger, from the 
Silurian of Gotland, the West of Ireland, and England; and 
G. Fletcheri, Hd. and H., from Dudley and Malvern. 
Lindstrém has made a careful investigation of the development of 
the septa in G. pyramidale, and has examined young specimens with 
a calicinal aperture of only 5 mm. in length by 4 mm. in breadth. 
The following are the results of his observations: (1) That in the 
young individuals septa are absent. (2) That the septum of the 
under-side is first developed, and may therefore be properly styled 
the primary septum. (3) That the median septa of the right and 
left sides are next formed. (4) That the median septum of the 
upper side appears last. (5) The lateral septa of the under-side are 
already developed before the median septa of the other sides appear. 
Thus the generally received opinion of four primary septa in rugose 
corals is not tenable, just as little as that four prominent septa are 
present in this group, when, as a general rule, they only occur in 
Goniophyllum and Stauria. 
The genus Argopoma, Lind., is represented by the single species 
A. prismaticum, Lind., from the Silurian of Gotland. In general 
appearance this species resembles a Cystiphyllum, but it is slightly 
sub-angular, and has an apparatus of four triangular valves with 
rounded corners. 
