20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



placed in Amplexopora and Acanthotrypella is considered a junior 

 subjective synonym of Amplexopora. 



AMPLEXOPORA SEPTOSA (Ulrich) 



PI. 5, figs. 1-2; pi. 6, figs. 1-3 



1879. Atactopora scptosa Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 2, 



p. 125, pi. 12, figs. 7-7C. 

 1882. Amplexopora scptosa (Ulrich), Journ. Cincinnati Soc. Nat. Hist., vol. 5, 



pt. I, p. 128; pt. 2, p. 255. 



Material studied. — The cotype suite of A. septosa, U.S.N.M. 43621, 

 contained a tangential thin section and a number of unsectioned 

 specimens. After sectioning, seven of the cotypes compared closely 

 with the original thin section and description of the species and are 

 considered to be conspecific. The remainder of those sectioned be- 

 long to other genera. The new^ U.S.N.M. catalog number of the 

 lectotype is 1 38281 ; paratypes and topotype are 138282 to 138288. 

 The primary types are from the Mount Hope shale member of the 

 Fairview^ formation, Maysville group, of the Upper Ordovician at 

 Covington, Ky. 



In addition, sections were made from topotype suites, U.S.N.M. 

 44912 and 44913, collected by E. O. Ulrich. 



Description. — Zoaria are ramose ; branches are circular to elliptical 

 in cross section. Conspecific overgrowth is common. Monticules 

 are high and nearly conical in outline. The inflection of zooecial walls 

 by acanthopores that characterizes the species can generally be seen 

 on exteriors of well-preserved specimens and seems to occur in ran- 

 domly arranged groups of zooecia. 



In the endozone, zooecial walls are extremely thin and are finely 

 crenulated to nearly straight. Diaphragms are generally sparse and 

 are concentrated in dome-shaped zones extending across the endo- 

 zones and in the outer regions of the endozones just preceding the 

 exozones. 



In the exozone, walls are relatively straight and moderate and 

 constant in thickness for the genus. In a few zooecia, short lengths 

 of wall vary in thickness. Zooecial boundaries in longitudinal view are 

 generally well-defined, dark, serrated lines or zones between abutting 

 laminae from adjacent zooecia. Laminae of adjacent zooecia generally 

 intersect the boundaries at angles much less than 90 degrees to form 

 a V-shaped pattern. A thin zooecial lining is common, and tends to 

 vary proportionally in thickness to the thickness of the diaphragm 

 immediately connected with the lining. 



