American Palceozoic Bryozoa. 



161 



literally covered with the detached segments, and man} r fine specimens 

 were secured, some of which preserve several hundred of the small 

 segments still in connection. As is shown by these specimens, each 

 segment at its upper extremity articulates almost invariably with two 

 succeeding segments, so as to produce a dichotomously branched 

 zoarium. The segments are about two tenths of an inch in length, 

 and less than one hundredth of an inch in diameter, and have, so far 

 as I could determine, always three series of cell-apertures, which are 

 situated in as many concave furrows. The fourth side is convex, and 

 wider than any of the other three sides, and is marked by from six to 

 eight distinct longitudinal strise. The cell-apertures, when perfect, are 

 provided with a delicate and prominently elevated rim; usualty, how- 

 ever, they appear as so many rounded apertures at the bottom of the 

 furrows. About nine cells occupy the space of .1 inch, and they are 

 separated from each other a little more than their own diamater. 



Arthronema tenue occurs in the Upper Trenton strata, of Kentucky, 

 and is a common fossil in the lower half of the Cincinnati group. 



Arthronema curtum, n. sp. (PI. VI., fig. 9.) 



The segments of this species differ from those of A. tenue, in being 

 stronger, shorter, and more finely striated on the non-poriferous side ; 

 besides the articular faces at each end are more distinctly enlarged. 

 The only specimen that I have seen presenting the poriferous side to 

 view is considerably worn, and all that I can say of the cell-apertures 

 is that they appear to be arranged in four series. Length of a single 

 segment, .09 inch ; diameter of same, .025 inch. 



Formation and locality : In the Cincinnati group, at an elevation of 

 from 250 to 300 feet above low-water mark in the Ohio river, on the 

 hills west of Covington, K}'. Rare. 



Arthroclema spiniforme, n. sp. (PI. VI., figs. 10, 10a.) 



Zoarium composed of numerous segments, which are cylindrical, por- 

 iferous on all sides, and pointed more or less obtusely at each end ; 

 their length varies from two to four tenths of an inch ; their diameter 

 from .015 inch to .04 inch. Cell apertures oblique, arranged between 

 slightly elevated longitudinal lines, and in transverse rows around the 

 stem. On account of their obliquit}', well preserved examples have 

 the lower margin of the aperture prominently elevated. There are 

 from eight to sixteen longitudinal series of cell-apertures around the 

 segments; seven of the transverse series occupy the space of .1 inch. 

 Longitudinal sections show that the cells radiate from a central axis, 



