NORTH AMERICAN LATER TERTIARY AND QUATERNARY BRYOZOA. 
123 
MICROPORELLA UMBONATA Hincks, 1882. 
Plate 36, figs. 6, 7. 
1882. Microporella ciliata forma umbonata Hincks, Report on the Polyzoa of the Queen Charlotte 
Islands, Annals and Magazine of Natural History, ser. 5, vol. 2, p. 15, pi. 17, fig. 1. 
„ » , (k=0.08 mm. 
Measurements .—Aperturab ^ 
Zooecia 
Lz— 0.52-0.60 mm. 
mm. l lz = 0.30-0.40 mm. 
Variations .—There is one small oral avicularium (rarely two). The frontal 
is a tremocyst with small pores. The ovicell is costulated. The frontal gibbosity 
(umbo) is always placed below the ascopore. Our specimens bear no spines. 
Affinities .—This species differs from Microporella ciliata Linnaeus, 1759, in 
the presence of the frontal umbo and in its larger micrometric dimensions. It 
differs from Microporella fallax Canu, 1904 from the post-Pampean of Argentina, 
which also bears a frontal gibbosity, in its avicularium which is placednotmuch 
below the ascopore but always at the same level with it. 
Occurrence. —Pleistocene: Santa Monica (rare), Santa Barbara (very rare), and 
Dead Mans Island, off San Pedro (very rare), California. 
Habitat .—Queen Charlotte Islands. 
Plesiotype. —-Cat. No. 68596, U.S.N.M. 
MICROPORELLA CALIFORNICA Hincks, 1883. 
Plate 36, figs. 8-10. 
1858. Lepralia californica Busk, Zoophytology, Quarterly Journal Microscopical Science, vol. 4, 
p. 310, pi. 11, fig. 6. 
1883. Microporella ciliata forma californica Hincks, Report on the Polyzoa of the Queen Charoltte 
Islands, Annals and Magazine Natural History, ser. 5, vol. 2, p. 444, pi. 17, fig. 3. 
1908. Microporella californica Robertson, The incrusting chilostomatous Bryozoa of the west 
coast of North America, University of California Publications, Zoology, vol. 4, No. 5, p. 281, 
pi. 18, figs. 32-34. 
fZz = 0.80 mm. 
Z 2 = 0.40-0.46 mm. 
Variations .—Our specimens are somewhat larger than those living to-day off 
the coast of California. There are six spines but on our fossils only two, three, or 
four alone persist. The frontal is a tremocyst with large pores superposed on an 
olocyst perforated by very small corresponding pores; it is detachable. 
The two avicularia are rather constant erect, rather long, very sharp, with a 
very fragile pivot; their slender beak is easily broken. In some cases one avicula¬ 
rium is smaller than the other. There is a salient frontal gibbosity bearing the 
ascopore or placed below it. The ascopore is surrounded by a smooth peristone. 
Hincks, 1883, thought that his specimens belonged to Busk’s species, 1856. 
Waters, 1908, affirmed that Busk’s species is Microporella coronata Savigny-Audouin, 
1826. 
Affinities .—This species much resembles Microporella coronata Savigny-Audouin, 
1826, in its costulate ovicell; it differs from it in the presence of six spines (and not 
four) and in its larger avicularia. It differs from Microporella ciliata Linnaeus, 
1759, in the constant presence of two large avicularia, and in its frontal with large 
tremopores. 
,, , . 7ia = 0.07 mm. 
Measurements .—Apertura 7 _ 10 
1 \la = 0.13 mm. 
Zooecia 
