192 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
3. On the inner face there are large cavities which, as they are closed by the 
ectocyst, are indeed hydrostatic. We have not been able to make zoarial sections 
of such a nature that we can see by what mechanism the sea water enters or departs. 
4. The mandibles of the oral avicularia are identical with those of the avicu- 
laria of the inner face. 
5. The ovicells observed were marginal and not inserted between the other 
zooecia, but our specimens are insufficient to note if this is a constant character. 
6. This species is very close in its dimensions to Mamillopora tuberosa Canu 
and Bassler, 1919, and differs only in the position of its ovicells and in the con¬ 
stancy of its oral avicularia. 
We do not know the inner side of Mamillopora smithi Calvet, 1907. That of 
Mamillopora cupula Smitt, 1872, has not been figured, but Smitt speaks of “a thin 
layer of bladders (aborted avicularia) on the back of the zooecia,” a description 
which appears to accord with our observation. Smitt’s specimens were deprived 
of the ectocyst and he was not able to determine the true nature of the avicularia. 
MAMILLOPORA TUBEROSA Canu and Bassler, 1919. 
Plate 6, figs. 16-19; plate 7, figs. 1-8. 
1919. Stichoporina tuberosa Canu and Bassler, Geology and Paleontology of the West Indies, 
Bryozoa, Publications of the Carnegie Institution of Washington, no. 291, p. 98, pi. 1, 
figs. 20-23; pi. 6, figs. 16-19; pi. 7, figs. 1-8. 
Description. —The zoarium is free, conical, hollow, with very thick walls. 
The peristome is salient, ornamented with small tuberosities; it bears one or two 
small, elliptical avicularia with bar or denticles. The apertura is elliptical, elongated, 
hidden at the base of a short peristomie; it is formed of a large, semielliptical anter 
and of a small, concave poster, separated by two small, salient cardelles. The 
ovicell is large, somewhat salient, convex; it is hyperstomial and always closed by 
the operculum. A salient, elliptical avicularium, with two denticles serving as 
pivot, is placed at the base of each zooecium; it deforms the adjacent peristomes. 
The inner side is tuberose and bears very large pores arranged in quincunx. On 
the lower face there are large pores surrounded by very small ones. 
,, , , . I k = 0.14 mm. ^ . f Lz =0.30 mm. 
Measurements. —Apertura w a _q jq 
mm. 
Zooecia 
lz =0.30 mm. 
Opesium of j ho = 0.10 mm. . . , . f Lav = 0.20 mm. 
avicularium j lo =0.06 mm. 1 V1CU anum j l av =0.12 mm. 
This is a very elegant species characterized by its peristomial tuberosities. 
The ancestrula is visible only in the interior of the zoarium; it is covered exteriorly 
by the first zooecia. All the zooecia are separated from each other by small canals 
which appear to end in the large, inferior pores. The oral tuberosities are hollow. 
The pores of the internal cavity are avicularia, of which the pivot is formed by two 
denticles; they are analogous with those of the external face (inferior). The 
internal face (and upper) bears also large cavities which we believe to be hydrostatic 
cavities; but it must be proved that the ectocyst is resistant enough to confine an 
equal amount of water. We must suppose also that these cavities are intended to 
counterbalance the irregularities of calcification and to assure the perfect equilibrium 
of the zoarial system. 
