120 
BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
developed, the tremopores appear large (forma praeciliata). A specimen from 
Carteret County, North Carolina, is very suggestive. The incrusting portion 
shows normal zooecia with granulations and tremopores (fig. 1)^ a bilamellar 
expansion shows, on the contrary, zooecia without granulations but with large 
tremopores (fig. 2). A specimen from Santa Barbara, California, has very small 
avicularia as in Microporella umbonata, but nevertheless its dimensions are ab¬ 
solutely identical with Microporella ciliata. 
,, . . , \ha = 0.04-0.06 mm. r/ . Lz = 0.50 mm. 
Measurements. —Apertura 7 Zooecia 7 _ „„ 
r l la = 0.10-0.12 mm. [te = 0.30mm. 
The coast of California is the Elysium of the genus Microporella, for a wealth 
of species occurs there. They are very closely related and their determination 
is not made without difficulty because of their polymorphism. It is necessary 
especially to take into consideration the reciprocal place occupied by the avicula- 
rium and the ascopore; the micrometric measurements are of value only in extreme 
cases. 
Occurrence. —Miocene (Choctawhatchee marl): Jackson Bluff, Ocklockonee 
River, 25 miles southwest of Tallahassee, Florida (rare). Miocene (St. Mary’s 
formation): Cove Point, Maryland (rare). Miocene; Kuhns, Carteret County, 
North Carolina (rare). Miocene (Choptank formation); Jones Wharf, Maryland 
(rare). Pleistocene: Santa Monica (rare); Dead Mans Island, off San Pedro (rare); 
and Santa Barbara, California (rare). 
Geological distribution. —Stampian of Germany (Schreiber); Chatian of Ger¬ 
many (Reuss); Miocene of Australia (Waters),'of Tunis (Canu); Burdigalian of 
Gard in France (Canu collection); Helvetian of Italy (Seguenza Neviani), of France 
(Canu collection); Tortonian of Italy (Seguenza), of Austria-Hungary (Reuss); 
Sahelian of Oran (Canu collection); Zanclean of Italy (Seguenza); Pliocene of 
New Zealand (Waters); Plaisancian of Algeria (Canu), of Italy (Manzoni), of 
England (Busk); Astian of Italy (Seguenza); Sicilian of Italy (Seguenza, Manzoni, 
Neviani), of Rhodes (Manzoni); Quaternary of Italy (Waters, Seguenza, Neviani, 
De Stefani). 
Habitat .—Cosmopolitan. 
Plesiotypes. —Cat. Nos. 68584-68590, U.S.N.M. 
MICROPORELLA HEXAGONA, new species. 
Plate 20, figs. 14, 15. 
Description. —The zoarium incrusts shells. The zooecia are little distinct, 
separated by a furrow, short, hexagonal,convex, gibbose; the frontal is convex, 
irregular, and formed of a tremocyst with large pores detachable from a subjacent, 
finely perforated olocyst. The apertura is deeply buried, semilunar; the peri¬ 
stome is somewhat salient, very thin, and bears four to six large, hollow spines. 
The ovicell is little salient and is covered by an incomplete tremocyst. The asco¬ 
pore is large and is surrounded by a verj 7 ; salient peristome. There are two small 
avicularia or a single one very large and salient. 
Measurements. —Apertura; 
ha = 0.07 mm. 
Za = 0.12-0.15 mm. 
Zooecia 
Lz = 0.45-0.50 mm. 
Zs = 0.45 mm. 
