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 ^nperpused tremopores (fig. 21). 



Occurrence. Middle Jacksonian : Baldock, Barnwell County, South Carolina 

 (very common) ; Eich Hill. Crawford County, Georgia (common) ; 18 miles west 

 of Wrightsville, Georgia (common). 



Upper Jacksonian (Ocala limestone) : Alachua. Florida (rare). 



Cotypes.CsA. No. 04153, U.S.N.M. 



PORELLA CKASSOPARIES, 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 sernilunar, 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 hyper- 

 stomial and opens into the peristomie. The median avicularinm is sunk in the 

 thickness of the tremocyst; it opens into the peristomie where it often forms a 

 tubular prominence. 



MCI/XI/I ' in, nt*. Apertura f Aa= 0.12 mm. Peristomicef hpe=Q.~20 mm. 



(interior) [ Z=0.15 mm. ( exterior) | fye=0.14 mm. 



. \Lz= 0.64-0.70 mm. 

 /ooecia, 7 



1/3=0.36-0.44 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. IS) ; the avicularium is 

 only visible there as a small convexity below the apertura. The abrasion of the 

 olocyst (fig. 19) shows 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). 



