NORTH AM KKirAN EARLY TERTIARY BRYOZOA. 1(51 



* = 



Zooecia 

 =0.16 nnn. 17^=. mm. 



. (La.f=O.B5 mm. 

 Avicularia , 



[fV=Oi20-0.25 mm. 



Affinities. The presence of the gymnocyst modifies the zooecial length very 

 much, and it is not rare to observe zooecia 0.60 mm. in length. The difference 

 between this form and .4. ft/minni/m is small: the mural rim is not complete and 

 the larger aricularium is terminated only by a beak having a small narrow canal. 



Many zooecia have no cryptocyst and these have considerable resemblance to 

 Cdllopora tenuirostri-s Hinck-. l^su. Imt this variety is not common enough to cause 

 errors in identification. Figure ?> on plate 30 is of a specimen altered chemically. 

 Figure -2 i^ perhaps of this species representing the region of the ancestrulu. 



Occurrence. Upper Jacksonian (Ocala limestone) : Old Factory, li miles 

 above Bainbridge, Georgia (very rare); 4 miles below Bainbriclge, Georgia (very 

 rare): 7 miles above Bainbridge. Georgia (very rare); Bainbridge, Georgia (very 

 rare). 



Cotypes.C&i. Xo. r>:Ml. U.S.N.M. 



AMPHIBLESTRUM ORBICLLATUM, new species. 



I'hite .>0, fig. 4. 



Description. The zoarium incrusts shells. The zooecia are distinct, little 

 elongated, suborbicular, separated by a deep furrow; they are surrounded by a 

 small gymnocy-t : the mural rim is thin and salient; the cryptocyst is flat, orbicular. 

 perforated with very scattered tremopores. The opesium is semilnnar, surrounded 

 by a salient peristome, the distal part of which bears from 4 to G spines. The ovicell 

 is hyperstomial. globular and salient; it opens above the operculum by a special 

 orifice. The small avicularia are rare, interzooecial. and triangular. There are two 

 pairs of lateral dietellae. 



. |^o=0.05 mm. . (3= 0.35-0.40 mm. 



Measurements. Opesia., , ,,_ Zooecia L . 



|/ec=0.0i mm. l?s=0.32-0.3o mm. 



Ajfiiiitii-'A. The genus Thulroporfi was jn'oposed by MacGillivrav in 1^00 for 

 the species provided with a calcified cryptocyst and with an opercnlum corre- 

 sponding to the opesium. This is precisely the case in our American species where 

 the opesium is transformed into a real aperture. But the species of Thn'ir<.ix>r<i 

 have some characters entirely different, such as interzooecial avicularia, internal 

 spicules, and labial processes. We are therefore unable to classifv this American 

 species in that genus. 



In its external aspect this species resembles a Mi<-, n/mi n. but it dilier- from 

 that genu~ in its hyperstomial. not endozooecial ovicell. and in the absence of 

 opesiules. 



In the ensemble of its characters, interopesial avicularia. oral spines, hvper- 

 stomial ovicell. this is surely an AmpfiiMrxfi-iim. of which it forms a very divergent 



'.i l;i Bull. 101! - 11 



