NORTH AMERICAS, EARLY TERTIARY BRYOZOA. 545 



Variations. In the recent species of this genus calcification is rather regular, 

 and the upper segments of the zoarium are essentially identical with the lower 

 ones. This is not the case with Tubi/<-< //</>'></ r/'cksburf/ica, where the progress of 

 calcification is not equal in either one or the other. This has resulted in very dif- 

 ferent external aspects, but it is easy to find good intermediate stages, for, fortu- 

 nately, the species is not rare. 



On the young zooecia the peristome is very salient (figs. 2, 3) or slightly 

 salient (fig. 4) : the pores are then disposed at the base of the small longitudinal 

 canals. The peristome is thicker on the intermediate specimens (fig. 15), and on 

 the segments of the base of the zoarinm it is very large and hides all of the peristo- 

 miale (fig. 8). 



The system of ramification is very remarkable. The zooecium bears in place 

 of the usual peristomie an enormous, very prominent apophysis perforated by two 

 (fig. 15) or four (fig. 8) very large pores. The base of the branched segments 

 presents the same disposition of two (fig. 11) pores. We must therefore admit 

 that the segments are thus united to each other by means of a corneous double joint : 

 the apophysis with four pores bears perhaps two segments of ramification. At the 

 end of the segments the branching takes place in the same manner, but without 

 prominent processes (fig. 8). The zooecia which branch and articulate in this way 

 are unprovided with an ascopore. We have attempted a restoration (fig. 1) of the 

 base of the. zoarium; the number of specimens did not permit us to complete it with 

 young segments. The latter bear only a single pore at their base and are joined 

 to the other segments only by a single chitinous joint, according to the general rule. 



The tubules are not cylindrical; their diameter is augmented without cessation; 

 consequently the frontal pores are smaller on the young segments (figs. 3, 4) than 

 on the old segments (figs. 8, 15). The progress of this calcification deforms the 

 zooecia and the peristomiale is separated from the frontal by a small furrow. 



There are six longitudinal rows of zooecia to each segment. 



The longitudinal section (fig. 13) unfortunately does not include an ovicell. 



The tangential thin section (fig. 16) shows a tremocyst, of which the pores are 

 separated by a complex and very characteristic network. 



In the interior (fig. 13) we note a very thin olocyst, of which each small per- 

 foration engenders a funnel-shaped tubule. This same arrangement may be easily 

 studied on the living specimens. This sort of tubule may not be ramified as in 

 Myriosffum, since its successive widening offsets the increase of volume. 



Tubiecellaria vicksbwrgica is one of the most notable species of the ancient 

 early Tertiary Gulf. 



The great distribution of this species in the Vicksburgian occasions its name. 



Occurrence. Yickshurgian (Marianna limestone) : West bank Coneciih River. 

 Escambia County. Alabama (common) : 1 mile north of Monroeville. Alabama ( very 

 common) ; Salt Mountain. 5 miles south of Jackson. Alabama (rare) ; Murder Creek, 

 east of Castlebury, Alabama (rare). 

 5589919 Bull. 106 35 



