118 THE VOYAGE OF H.M.S. CHALLENGER. 
2. Agaricia frondosa, Duchassaing. 
Agaricia frondosa, Duchassaing, Revue des Zooph. et Spong. des Antilles. 
Duchassaing and Michelotti, Suppl. Mem. Cor. des Antilles, pl. x. figs. 5, 6. 
” ” 
A single specimen of this species was obtained. It agrees very closely with the 
figures given by the authors, except that the magnified calicles are drawn with too many 
septa, there being seldom more than thirty. It bears a close resemblance to the young 
specimens of Agaricia agaricites, but instead of the evenly arranged, seriate calicles 
characteristic of that species, the calicles are closely placed but irregularly arranged, 
raised or depressed, and the synapticulate walls do not form thick, solid, sharp-edged 
crests. 
Locality.—St. Thomas. 
3. Agaricia regularis, nu. sp. (Pl. V. figs. 7-7). 
Corallum explanate, more or less incrusting, with a wide, free edge; extremely solid, 
from 5 to7 mm. thick quite close to the margin, becoming quite thick at the central part ; 
the margin very sharp-edged. The under surface irregularly and faintly undulate, with 
distinct, sharp, more or less concentric edges as though produced by separate lines of 
growth, faintly and finely striate with very closely crowded, minute, regular, radiate 
costee. Upper surface somewhat unevenly raised and depressed, with calicles some- 
times arranged in irregular, more or less distinct series, but never elevated at the 
lower border so as to become oblique. Calicles generally irregularly placed, sub- 
circular or subpolygonal, small, from 1°5 to 3 mm. in diameter, rather shallow, close, 
even at the margin, separated by rounded interstices which are quite narrow or rather 
broad (from 1 to 2°5 mm. wide) over which the septa are continuous from centre to centre. 
Three cycles complete, a fourth often present and incomplete. The septa are small, 
granulated, very thin and even, appearing like striations on the surface. Columella 
small, tuberculate. Synapticulee small, thin, and very distinct in the marginal calicles 
where they are regularly placed and parallel; but becoming closer and thicker on the 
more central parts, and eventually fusing to form a solid wall. Endotheca very 
slightly developed, rudimentary. 
The species is represented by a fragment about 9 em. long. 
The form differs from the other known species of Agaricia in the much more 
scattered arrangement of the calicles ; but this affords no grounds for generic separation 
since the arrangement of the calicles is extremely variable in the genus. It seems to 
have a close resemblance to the Agaricia planulata, though differing in numerous 
characters from that species. 
A striking feature of the species is the nature of the synapticulee, which are extremely 
