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BULLETIN 125, UNITED STATES NATIONAL MUSEUM. 
on a median prominence of the frontal. The avicularium is short, triangular, with¬ 
out pivot, with its beak turned toward the top. The dietellae are not entirely 
covered over, and appear between the zooecia in the form of small slits. The 
ovicell is large, globular, buried in the distal zooecium, covered with a tremocyst. 
Measurements. —Aperturaj 
Aa = 0.10 mm. 
Za = 0.10-0.12 mm. 
„ . \Lz = 0.60 mm. 
Zooecia 7 _ __ 
te = 0.50 mm. 
Variations. —In this genus, where the species are so difficult of determination, 
the present species is very well characterized by the dietellae not entirely covered 
over by the tremocyst. We are ignorant as to the cause of this remarkable pecu¬ 
liarity, which has been observed hitherto only in the Membraniporae. The distal 
diatellae are visible on the marginal zooecia. The two proximal spines are always 
larger and more salient than the distal spines. Our micrometric measurements are 
those of the larger zooecia for the variations are considerable. 
Occurrence. —Miocene (Yorktown): Near Macedonia Church, Essex County, 
(very rare); 1 mile northeast of Suffolk, 3 miles southwest of Petersburg, and other 
localities in Virginia. Miocene (Duplin marl): 10 miles south of Greenville, North 
Carolina (rare). 
Cotypes. —Cat. Nos. 68593, 68594, U.S.N.M. 
MICROPORELLA TESSELLATA Tuomey and Holmes, 1857. 
Plate 30, figs. 2, 3. 
1857. Cellepora tesselata Tuomey and Holmes, Pliocene fossils of South Carolina, p. 13, pi. 4, fig. 7. 
Measurements. —Aperturaj 
ha = 0.06 mm. 
Z<x = 0.11 mm. 
Zooecia 
Lz = 0.75 mm. 
Zz = 0.60 mm. 
Variations. —There are often six very short and very inconstant spines. The 
vestibular arch is always visible. The apertura is relatively small for so large a 
species, which appears to indicate extremely fine tentacles. The frontal is per¬ 
forated with rather large tremopores. The ascopore is surrounded by a salient 
peristome. In the vicinity of the ancestrula the avicularium is small and placed 
at the level of the ascopore. The large marginal zoeceia have their avicularia 
larger and placed in the wider part of the zooecium well below the ascopore. This 
character is quite visible on the figure of Tuomey and Holmes and we believe that 
it is sufficient to recognize this long-forgotten species of these American authors. 
There are six lateral and one distal dietellae. 
Affinities. —This species differs from Microporella eustomata Gabb and Horn, 
1862, and from Microporella vibracvlifera Hincks, 1883, in its smaller avicularium, 
more distant from the zooecial axis and of a more irregular position. It differs from 
Microporella ciliata Linnaeus, 1759, in the large zooecial dimensions and its larger 
avicularium. 
Occurrence. —Pliocene (Waccamaw marl): Waccamaw River, Horry County, 
and Giles Bluff, Peedee River, South Carolina (Tuomey and Holmes). 
Pleisotypes. —Cat. No. 68595, U.S.N.M. 
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