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. G. 

 1908. MembTani'poTa horrida Robertson, The incrusUng 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. 7 Membranipora californiensis Waters, Observations on Membranipoadae, Journal Linnean 



Society Zoology, vol. 2G, p. 681, pi. 49, fig. 14. 



^ . (7(0 = 0.28-0.30 mm. „ Ji2 = 0.50mm. 



ifeasuremente.— Opesia|^^_Q_^g_Q_^g ^^^ ^°°®"^|Zz = 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 californiensis Waters, 1898, presents six articulated areal spines; 

 our form is therefore intermediate between Waters' species and that of Hincks. 



This species differs from Membranipora occuUata Robertson, 1908, in shorter 

 opesium, and in its larger and differently placed avicularium. 



Occurrence. — Pleistocene: Santa Barbara, CaUfornia (rare). 



Habitat.^Enstevn 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 circinndathrata HiNCKa, 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. •„ e *i, 



1908. Membranipora circumclathrata 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 opercidum. 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 m the 

 separating furrow of two zooecia; it is clearly attached to one of the mural runs and 

 it is perhaps the base of a pedunculate avicularium as is the genus Cauhramphus. 

 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. 



