NO. 5 ORDOVICIAN BRYOZOA — BOARDMAN 5 



SYSTEMATIC DESCRIPTIONS 



Genus BATOSTOMA TJlrich 



1882. Batostoma Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 5, pt. i, p. 154; 



pt. 2, p. 256. 

 1890. Batostoma Ulrich, Illinois Geol. Survey, vol. 8, pp. 379, 459. 

 1893. Batostoma Ulrich, Geology of Minnesota, vol. 3, pt. i, pp. 288-290. 

 1893. Stromatotrypa Ulrich, Geology of Minnesota, vol. 3, pt. i, pp. 301, 302. 



Type Species. — Monticulipora {Heterotrypa) implicatum Nicholson, 

 1 88 1, by monotypy. 



Emended definition. — Zoaria are ramose or incrusting and mon- 

 ticules are generally low. Zooecial walls in the endozones are thin, 

 dark, and granular and are connected directly with the well-defined, 

 dark, granular, slightly serrated zooecial-mesopore boundaries of 

 the exozones. In the exozones, zooecia are generally oval in cross 

 section and contain thin, laminated, irregularly spaced diaphragms. 

 As seen in longitudinal sections, the laminae of adjacent zooecial walls 

 lie nearly parallel to the zooecial boundaries, then curve distally just 

 before intersecting the boundaries to form a V-shaped pattern that 

 has extremely long, convexly curved limbs. In tangential sections, 

 walls of adjacent zooecia are generally integrate in appearance. 



Mesopores are polygonal in cross section, filling the spaces between 

 zooecia. Laminated wall material on the mesopore sides of boundaries 

 is generally thinner than on zooecial sides, and is lacking entirely in 

 earlier growth stages of several species. Mesopores contain closely 

 spaced diaphragms that generally are curved convexly outward. 

 Larger mesopores have more than one longitudinal row of curved 

 diaphragms that together form a flattened cystose pattern. Mesopore 

 diaphragms are generally thicker than those in zooecia and consist 

 of a thin, dark, granular layer on proximal sides and a thicker 

 laminated layer on distal sides. Acanthopores are variable in size 

 and abundance, and in a few species are very rare. 



Discussion. — Based on an examination of thin sections of primary 

 types of species now assigned to Batostoma in the U. S. National 

 Museum collections, the following species are considered to belong to 

 that genus: 



B. cumingsi Loeblich, 1942, Bromide formation. Middle Ordovician, Oklahoma. 

 B. fertilis Ulrich, 1886, lower half of the Trenton shales. Middle Ordovician, 



Minnesota. 

 B. fertile var. circulare Ulrich, 1893, lower third of the Trenton shales. Middle 



Ordovician, Minnesota. 

 B. manitohense Ulrich, 1889, Stony Mountain formation. Upper Ordovician, 



Manitoba. 



