New Lower Silurian Bryozoa. 



NEMATOPORA OVALIS, n. Sp. 



I 9 7 



Fig. 21. — Nematopora ovalis, n. sp. a, fragment of the natural size and xl8, with 

 rive ranges of zooecia. b, another with more ridges, only four rows of zocecia, and 

 the apertures less closely arranged. 



Zoanum ramose ; branches bifurcating at intervals of about 2 

 mm. ; 0.3 to 0.4 mm. in diameter, subquadrangular or pentagonal 

 in cross-section, each face with a row of zocecia. Zocecial aper- 

 tures direct, very large, oval, nearly 0.3 mm. long by 0.15 mm. 

 wide, enclosed by a sharply denned peristome. A short ridge 

 joins the peristomes of each row of apertures, and longitudinally 

 divides the concave spaces between the ends of the apertures. 

 These spaces are larger in the subquadrate examples than in those 

 having five rows of zocecia. They also have the thin ridge that 

 bounds each face more distinct from the elevated margins or 

 peristomes of the. zocecial apertures, which, in the pentagonal 

 specimens, to a large extent also form the border of the faces. 

 Longitudinal interspaces generally shorter than the length of the 

 zocecial apertures; about five of the latter in 2.5 mm. 



The large zooecial apertures serve to distinguish this species 

 from all the others known to belong to the genus. Under the 

 microscope the general appearance of the zoarium is strikingly 

 different from that of N. granosa, with which it is associated. 



Position and locality : Top of Trenton Shales, Cannon Falls, 

 Minn. 



