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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
often between them. The septal margins are dentate; the septa themselves are perforate. 1 The 
columella is represented by a small tubercle or lamina. 
Forma 0, PL xxxiii and xxxiv, fig. 2. — This form is represented by two specimens. Its most 
striking peculiarity is the fewness of gibbosities, but correlated with this character are others. When 
the surface is gently rounded, the calices are smaller than in forma a, being only 1 mm. in diameter, 
the walls separating the corallites are often not so acute as in forma a, and the calicular fossa resembles 
a pit with a perpendicular boundary. It at first sight seem? that two distinct species are represented, 
but there are gibbosities present in forma 0, and upon these the calicular characters of forma a 
appear. The calices here are larger, between 1.5 and 2 mm. in diameter, the separating wall between 
adjoining calices acute, etc. These specimens are a good illustration of the possibility of dividing one 
species into two, should only portions of the surface of the coralla be studied. They illustrate, too, 
the influence of form of growth upon the size and other characters of the calices. While the calices 
on the gibbosities are large, those situated in the depressions between them are small, only a milli- 
meter or even less in diameter. 
The actual arrangement of the septa of Porites astreoides forma a is similar to that of P. porites, i. e., 
there is a solitary directive septum with a group of three septa opposite, and besides these there are 
four pairs of septa, two pairs on each side of the plane of symmetry, except that the septa of the 
group of three remain free one from another and are prolonged to the columella each independently; 
the outer two septa of those three bend toward the included one. Twelve is the usual number of septa, 
though sometimes there may be a few more. The arrangement of the septa, columella, etc., are 
frequently the same in both formse a and 0. As the calices of the latter are usually deeper than in 
the former, a photograph did not bring out the structural features clearly. Pali are poorly developed 
or absent. 
Classifying the calicular structure according to Bernard’s 2 scheme, which has been already referred 
to, the usual plan is represented by his fig. 2 or is intermediate between figs. 1 and 2. 
In forma a the condition represented by fig. 1, where the inner margins of all septa are free one 
from another, was not found, but in some calices the fusion was slight; fig. 2 represents the usual 
condition; the condition represented in fig. 4 was found in a few instances, but the pali were poorly 
developed. In forma 0 the condition represented by fig. 1 is frequently approached very closely, if not 
actually present; that of fig. 2 is represented; and that of fig. 4 is hinted at, but not clearly present. 
Bernard has published some notes on the calicular structure of P. astreoides in his paper already 
cited on the calices of the genus. 2 
Class HYDROZOA. 
Order HYDROCORALUNtE Moseley . 3 
Family MILLEPORID^E L. Agassiz. 
Genus MILLEPORA Linnaeus, 1758. 
Millepora alcicornis Linnaeus. PI. xxxv-xxxviii. 
1758. Millepora alcicornis, Linnaeus, Syst. Nat., ed. x, p. 791. 
1880. Millepora alcicornis, Pourtal&s, Mem. Mus. Comp. Zool., vol. vii, No. I, pi. xx, figs. 1-6 (all figs.). 
1898 . Millepora alcicornis, Hickson, Proc. Zool. Soc. London, for 1898, p. 256 (vide pp. 245-257). 
Hickson (op. et loc. sup. cit) has given a lengthy discussion of the synonymy of this species. 
Following him I have not recognized more than one species of Millepora in the West Indies. Two 
distinct forms, as determined by the shapes of the coralla, are represented in the collection; one 
possesses a solid and palmate corallum, and the other has the corallum dissected, with some digitiform 
projections. Both forms are shown in the plates. 
From Mayaguez and Culebra. 
1 Bernard’s characterization of the septa of Porites as “ perforate lamellate septa ” (Jour. Linn., vol. xxvii, 1899, p. 137) 
is correct. 
2 Op. sup. cit., p. 492. 
8 These, although they are not corals, are included because they are among the commonest of the reef-building 
animals of the Porto Rican waters. 
