NORTH AMERICAN EARLY TERTIARY BRYOZOA. 559 



formed of thin, prominent interareolar costulcs, and of a false area due to incom- 

 plete pleurocystal calcification. The peristomie is of little depth; the peristome 

 is thin, prominent, developed distally only; the aperture (as seen from the interior) 

 is semilunar with an almost straight proximal border. The avicularium is median, 

 simple, triangular; its point projecting, like a spur. 



. f^=0.10mm. 1 . (3=0.50-0.60 mm. 



Measurements. Penstomice { , Zooeciai, n - 



U/>=0.10 mm. Us=0.25-0.30 mm. 



Observation. Photography does not give exactly the aspect of this species; 

 it does not show sufficiently the very great projection of the avicularium above the 

 plane of the figure. 



Bracebtddgia aculeata differs from the other known species by its straight and 

 median avicularium. which is never oblique, or sublateral. 



In the interior the avicularium is invisible, and it is therefore of exterior or 

 pleurocystal origin. 



Occurrence. Middle Jacksonian: Three and one- fourth miles south of Perry, 

 Georgia (common). 



Cotypes.Cat. No. 64188, U.S.N.M. 



BRACEBRIDGIA POLYMORPHA Reuss, 1864, var. COSTULATA, new variety. 



Plate 71, figs. 13-23. 



1864. Eschara polymorpha RKUSS, Fauna deutschen Oberoligocau, Sitzungberichte der k. 



Akademie der Wissenschaften, Wien, vol. 50, p. 651. pi. 12. fig. 6. 

 1868. Eschara polymorpha Ricuss, Bryozoa deutschen Septarieuthones. Sitzungberlchte der 



k. Akademie der Wissensehaften, Wien, vol. 52, p. 61. pi. 8, figs. 8-10. 

 1867. Eschara polymorpha REUSS, Fauna Steinsalzablagerung. Sitzungberichte der k. Akade- 



mie der Wissensehaften, Wien, vol. 55. p. 144. 



.. 



Measurements. Aperture], rt ir> 



(la=O.W mm. 



Variations. The areolae form a line of small pores around each zooecium (figs. 

 15, 20). Between them short costules often develop (figs. 17, 20). 



The pleurocyst is not very regular; it forms a prominent collar around each 

 zooecium, in the form of an interrogation point. Below the avicularium there is 

 an irregular, triangular area, the depth and size of which depends upon the pleu- 

 rocystal activity, which is always very irregular. 



The avicularium. when it is well preserved, deforms the external aperture 

 (figs. 15, 18, 21) ; it is oblique (figs. 15, 18) or transversal (fig. 17) : the two posi- 

 tions may be observed on the same zoarial fragment (fig. 21). 



The gonoecia (figs. 14, 22) are larger than the usual zooecia. 



All these characters are lessened by fossilization (fig. 23) and the zooecia 

 appear very polymorphic. 



1 In the Adeonidae we give the dimensions of the peristomice or external aperture when this is somewhat 

 constant, in preference to the dimensions of the apertura which can be measured only in the interior of 

 the zooecia. 



