American Palaeozoic Bryozoa. 



159 



and genus is found, was collected from strata of the Trenton group, 

 near Knoxville, Tenn. 



Mitoclema cinctosa, nov. gen. et sp. (Plate VI., figs. 7, la.) 

 Mitoclema, gen. char, ante p. 150. 



Zoarium ramose, branches very slender, and divided dichotomously 

 at intervals, varying from less than one quarter inch to one half inch. 

 Cells radiating from an imaginary central axis, with the apertural 

 portion tubular and partially free; cell apertures rounded, and 

 arranged in transverse series around the branches; there are eight of 

 these rows in the space of .3 inch ; and from twelve to fifteen cell 

 apertures in each series. Diameter of branches about .035 inch. 



Mitoclema bears considerable resemblance to the Mesozoic and 

 recent genera Spiropora, Larax., and Entalophora, Lamx., and doubt- 

 less belongs to the same family of Bryozoa. However, neither those 

 genera nor any other genus of the Entalophoridce is known to occur in 

 older strata than Jurassic. Another species of Mitoclema occurs in 

 the Trenton rocks of New York, which (if I have correctly identified 

 the form) was described by Hall under the name of Gorgonia ? 

 perantiqua. (Pal. N. Y., vol. i, p. 76, 1847.) 



Formation and locality: This species was collected by Prof. A. G. 

 Wetherby and the author, at the bottom of the gorge of the Kentucky 

 river, near High Bridge, Ky. Trenton. 



Fenestella oxfordensis, n. sp. (Plate VI., fig. 13.) 



Zoarium broadly, and usually incompletely funnel-shaped ; branches 

 slender, five or six in the space of .1 inch, regular, and somewhat rigid 

 in appearance; on the non-poriferous side they are rounded, and 

 apparently always smooth. Dissepiments about one half the width of 

 the branches, and expanding at their junction; five or six in the space 

 of .1 inch. Fenestrules elliptical to sub-quadrangular, with a width 

 about equal to that of the branches, and a length from once and a half 

 to twice the width. Cell-apertures in two ranges, one on each side of 

 a moderately developed median ridge, generally three in the space of 

 each fenestrule, circular, and distant from each other usually less than 

 half their diameter. A small node appears to be developed on the 

 median ridge at the point of junction of the dissepiments with the 

 branches. 



This species is the only undoubted one of Fenestella, known to me 

 from American Lower Silurian rocks. It is related to both F. prisca, 

 Lonsdale, and F. tenuis, Hall, from the Clinton group of New York. 



