NORTH AMERICAN EARLY TERTIARY BRYOZOA. 



265 



nent; the opesiules are large, round, and dissimilar; the opesium is surrounded 

 by a small, improminent collar (oral arch). 



T, .-. fAo=0.30mm. 



Measurements. Opesium -L _ n , a zooecia 



/? zooecia |f 3=L25mm - 

 (is=0.60mm. 



Variations. This species is rather constant in its characters. 



[Zz=0.75-O.S5mm. 



, 



lfe=0.55mm. 



The partition 



which separates the two chambers is horizontal in the a and B zooecia, so that both 

 kinds of zooecia are provided with a polypide tube, a condition which does not 

 exist in the preceding species studied (Steganoporclla jacksonica, etc.) (figs. 3, 4). 

 The tube is seen complete after very gently rubbing away the surface of the 

 zoarium (fig. 5). 



The dissymmetry of the opesiules is constant, but it is not very great, and cer- 

 tainly the retractor muscles of 

 the polypide were not attached in 

 one of the proximal angles of 

 the zooecium. 



In this section it appeared 

 to us that the frontal was a 

 tremocyst resting on an olocyst, 

 but this is a point to be verified. 

 The zooecial mural rim is an 

 olocyst whose elements are 

 grouped in radial rows around 

 the opesium (fig. 6). 



The zoarium may attain a 

 length of 2 centimeters ; the size 







FIG. 72. Genus Siphonoporella Hincks, 1880. 

 A-D. Siphonoporella delicatissima Busk, 1840. A. View 

 of zooecia, X 40, with covering membrane removed. B. 

 Zooecium of same, X 75. C. Zooecium, X 75, showing 

 proximally directed part of polypide tube. D. View from 

 the basal surface, X 40. (A-D after Levinsen, 1909.) 



of the zooecia permits its deter- 

 mination with a simple hand 

 lens. This is a good-sized fossil 

 and can be readily employed in 

 field determinations. 



Occurrence. Vicksburgian (Marianna limestone) : West bank of Conecuh 

 River, Escambia County, Alabama (common) ; Salt Mountain, 5 miles south of 

 Jackson. Alabama (common) ; Murder Creek, east of Castlebury. Conecuh County, 

 Alabama (common) ; Claiborne. Monroe County, Alabama (common). 



Cotypes.C&t. No. 64257, U.S.N.M. 



Genus SIPHONOPORELLA Hincks, 1880. 



1880. Siphonoporella HINCKS, General History of Marine Polyzwi, I. Maileiran Polyzoa, 

 Annals Magazine Natural History, ser. 5, vol. 6, p. 22. 



The proximal calcified pad of the frontal wall is formed by a larger or smaller 

 arched gymnocyst; the aperture is not surrounded by a projecting margin; the 

 zooecia occurring only in a single form and provided with a small, always unarmed 



