NORTH AMERICAN LATER TERTIARY AND QUATERNARY BRYOZOA. 
43 
CALLOPORA HORRIDA Hincks, 1880. 
Plate 33, figs. 18, 19. 
1880. Membranipora horrida Hincks, Contributions towards a general history of the marine Polyzoa, 
Annals and Magazine of Natural History, ser. 5, vol. 6, p. 82, pi. 10, fig. 6. 
1908. Membranipora horrida Robertson, The incrusting Cheilostomatous Bryozoa of the West 
Coast of North America, University of California Publications, Zoology, vol. 4, No. 5, 
p. 260, pi. 4, figs. 3, 4. 
1898. ?Membranipora cali/orniensis Waters, Observations on Membraniporidae, Journal Linnean 
Society Zoology, vol. 26, p. 681, pi. 49, fig. 14. 
Measurements .—Opesia 
Zooecia 
\Lz = 0.b0 mm. 
ho = 0.28-0.30 mm. 
Zo = 0.16-0.18 mm. = 0.30-0.40 mm. 
Our specimens have two areal spines, sometimes four. They present micro¬ 
metric measurements a little different from those noted on Miss Robertson’s figure; 
it is difficult, however, to admit two distinct species, the other characters being 
very similar. In studying a recent specimen of this species we have been convinced 
that the orifice of the ovicell is very small and can not be closed by the operculum. 
Membranipora cali/orniensis Waters, 1898, presents six articulated areal spines; 
our form is therefore intermediate between Waters’ species and that of Hincks. 
This species differs from Membranipora occultata Robertson, 1908, in shorter 
opesium, and in its larger and differently placed avicularium. 
Occurrence. —Pleistocene: Santa Barbara, California (rare). 
Habitat .—Eastern Pacific: Pacific Grove (Robertson) and the Queen Char¬ 
lotte Islands (Hincks). 
Plesiotype. —Cat. No. 68456, U.S.N.M. 
CALLOPORA CIRCUMCLATHRATA Hincks, 1881. 
Plate 34, figs. 1-3. 
1881. Membranipora drcumclathrata Hincks, Contribution general history of Marine Polyzoa 7, 
Foreign Membranipora, Annals and Magazine Natural History, ser. 5, vol. 8, p. 131 (sep. 
72), pi. 5, fig. 1. 
1908. Membranipora drcumclathrata Robertson, The incrusting Cheilostomatous Bryozoa of the 
West Coast of North America, University of California Publications, Zoology, vol. 4, p. 259, 
pi. 14, figs. 1, 2. 
Structure .—In this species the ovicell is not closed by the operculum. Not 
only is this quite visible on the fossils but we have been able to verify it on a recent 
specimen dredged off Santa Monica. Sometimes a triangular pore is visible in the 
separating furrow of two zooecia; it is clearly attached to one of the mural rims and 
it is perhaps the base of a pedunculate avicularium as is the genus Cauloramphus. 
We have not observed these pores on our recent specimens. At the base of each 
opesium there is a small triangular avicularium with salient beak placed on the 
median zooecial axis. It sometimes becomes very large and is developed obliquely 
as in Callopora horrida Hincks, 1880. Nevertheless, the presence of wide-spaced 
areolar pores differentiates the two species clearly. 
Occurrence. —Pleistocene: Santa Monica (Long Wharf Canyon), California (rare). 
Habitat .—Pacific coast of California. 
Plesiotypes. —Cat. No. 68457, U.S.N.M. 
