574 



TRANS. ST. LOUIS ACAD. SCIENCE. 



ated from the root as a circular frond. The branches are com- 

 paratively broad, averaging a millimetre, or twice the breadth of 

 those of D. gracile^ and the transverse bars are comparatively 

 stout. The radicle or initial point is often well preserved. Two 

 specimens before me are about 12 centimetres high and 25 broad. 

 Few perfect specimens can be found. 



Formation and Locality . — In New. York it is found throughout 

 the Niagara shales at Lockport and elsewhere. In Canada, it 

 occurs at Grimsby and at Hamilton, in the somewhat earthy dolo- 

 m ites beneath the chert-bed. 



DlCTYONEMA GRACILE (Hall). 



Plate 2. Fig 2 represents a fragment, and Fig. 3 represents a celluliferous portion of a 

 frond enlarged (found at Hamilton). 



(Paleontology of New York, vol. ii.) 



'• Frond circular or flabelliform (probably cyathiform in its 

 growing state), composed of slender bifurcating and slightly di- 

 verging branches, which are united laterally and at long intervals 

 by very slender filaments ; branches irregularly striated or indent- 

 ed, sometimes having uneven or subserrate margins ; texture like 

 D. retiforme^ with an outer black filament and interior subcalca- 

 reous stipe." (Hall.) 



In this species the branches are much more slender than in Z>. 

 retiforme^ averaging about half a millimetre in breadth and twice 

 that distance apart. The branches are regularly arranged and 

 form fan-shaped fronds, but many specimens indicate the cyathi- 

 form structure while living. Though the margins are generally 

 even, yet in one fine specimen the terminations of the branches 

 are irregular. The fronds converge to what is evidently a non- 

 celluliferous radicle, and in size the finest specimens are as much 

 as lo centimetres high and 6.5 broad. 



The transverse filaments, which are non-celluliferous, are from 

 four to five times as far apart (sometimes much farther) as the 

 branches ; or are frequently obliterated, or almost so. The tex- 

 ture is corneous. 



The celluliferous structure is shown in very few specimens. 

 However, one specimen (Plate 2, fig. 3), in particular, which I 

 obtained from Mr. A. E. Walker of Hamilton, removes all doubt 

 as to the character of the cellules. On one side of the branch 

 there is a slender solid axis, in the other there are inserted cylin- 



