490 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
12) the determination remains rather difficult, and it is necessary to assemble a 
considerable number of specimens to make it. The thickness of the walls of the 
tubules is quite visible on the tangential sections (fig. 23). Their length is visible 
on the transversal sections, which are always difficult to make on account of the 
irregularity of the frontal network. The olocyst is perforated with very small 
pores corresponding to the superposed tremopores (fig. 21). 
Occurrence. — Middle Jacksonian: Baldock, Barnwell County, South Carolina 
(very common) ; Rich Hill, Crawford County, Georgia (common) ; 18 miles west 
of Wrightsville, Georgia (common). 
Upper Jacksonian (Ocala limestone) : Alachua, Florida (rare). 
Cotypes . — Cat. No. 64153, U.S.N.M. 
PORELLA CRASSOPARIES, new species. 
Plate 95. figs. 10-21. 
Description . — The zoarium is hollow, cylindrical, branched, unilamellar; it 
incrusts small algae. The zooecia are distinct, elongated, tubular; the frontal is 
convex and formed of a thick tremocyst with large tubules placed on a very thin 
perforated olocyst. The apertura is semilunar, very oblique, situated at the base 
of a deep peristomie; the peristome is thin or thick, hardly salient, interrupted in 
front. The ovicell is salient, globular, of the same nature as the frontal ; it is hvper- 
stomial and opens into the peristomie. The median avicularium is sunk in the 
thickness of the tremocyst; it opens into the peristomie where it often forms a 
tubular prominence. 
Measurements. — Apertura [ ha= 0.12 mm. Peristomicer hpe=0.20 mm. 
(interior) \la= 0.15 mm. (exterior) \Zpe=0.14mm. 
„ . fZs=0.6T-0.70mm. 
Zooeciaj fo=0 . 36 _ 0i 44 mm . 
Variations. — The great variations of this species evidently depend on the 
thickness of the tremocyst. The young zooecia (fig. 12) are bordered and appear 
smaller. The old zooecia (figs. 13, 14) appear larger; the avicularium is there 
little visible (fig. 13), and even invisible (fig. 14); the great thickness of the 
frontal may be seen in the transversal sections (fig. 21) and in the longitudinal 
sections (figs. 15-17) , where the tremopores are transformed into very long tubules. 
In the interior the lateral walls are very thin (fig. 18) ; the avicularium is 
only visible there as a small convexity below the apertura. The abrasion of the 
olocyst (fig. 19) shoves that it is very small. 
Figure 20, though badly oriented is however very interesting. On top the sec- 
tion is in the tremocyst and the pores are white. Below the section is in the 
olocyst for the pores are closed. The black rings indicate the section; on some 
pores we see the small pore which perforates the olocyst in the middle of the 
large ring formed by the tremopore. 
The zoarium may be formed of many superposed, lamellae (fig. 15). 
