BRYOZOA. 559 



morphic pores on the summit instead of the sides, and much 

 more numerous on the reverse. The branches are also more 

 rigid. The form described by me as Semicoscinium infraporosum 

 (Contr. Am. Pal. Vol. I, PI. I, 1886) has aU the characters of 

 Fenestrapora. It is from the Upper Helderberg group, and 

 differs from the two Hamilton species in its smaller size, strongly 

 undulated frond, flattened and comparatively strong reverse 

 aspect of its branches, and other points of minor importance. 

 Position and locality: Hamilton group; Buffalo, Iowa. 



HEMITRYPA Phillips, 1841. 



CPaL Foss. of Cornwall, Devon. & Westsomerset, p. 27.) 

 (For generic diagnosis see page 396.) 



For further discussions see chapter on classification, under the 

 section treating of the FENESTELLID.E (page 349). Of the four- 

 teen or more species known, one is from the Clinton, two from 

 the Lower Helderberg. one or more from the Hamilton, four 

 from the Keokuk and one or more from the Warsaw and St. 

 Louis limestone. 



HEMITRYPA TENERA Dlrich. 



PL XLIV, fig. 7 7a, and PL LIT, fig. 10 lOc. 



Zoarium infundibuliform, only known from fragments. The 

 obverse is a very delicate net-work in which the principal and 

 secondary bars are indistinguishable, being equal in width and 

 both zigzag: connected by lateral bars or scale? of the same 

 width, they form equal hexagonal interstices, arranged in very 

 regular vertical and diagonally intersecting series, twelve in 3 

 mm. measuring along the rows. Their openings correspond in 

 number to the zooecia in the branches beneath them. Zocecia 

 observed only in thin sections. On the reverse the branches are 

 straight or slightly zigzag, slender, thirteen or fourteen in 5 

 mm., rounded, somewhat variable in width, smooth when old, 

 granular and striated longitudinally when young. Dissepiments 

 short, in the middle about as wide as the branches, spreading 

 at their junction with them; on some portions of the zoarium, 



