SPENCER NIAGARA FOSSILS. 573 



margin ; branches and subdivisions united laterally by fine trans- 

 verse dissepiments ; branches impressed with deep stri£e of 

 grooves, producing indentations that sometimes have an elonga- 

 ted rhomboidal form ; axis subcalcareous, with a corneous ex- 

 terior." (Hall.) 



The branches generally appear as black threads on the stone, 

 but these can be distinguished from Fenestella by the corneous 

 character, even in indistinct fragments. In one species, at least, 

 I have seen the axis well represented. In D. gracile^ the cells 

 are circular or ellipsoid-cylindrical, extending into the coenosarc 

 or even common canal ; they are situated on one side of the stipe 

 only. In another species only oval pits mark the cell-apertures. 

 The striae are probably caused by the depression of the common 

 canal between (or at the junction of) the cellules, and thus rep- 

 resenting the general position of the polypite. In D. gracile 

 Prof. Hall represents the cell-orifices as characterized by denti- 

 cles ; in our collections this is not represented, although I have 

 a very fine specimen before me that shows the cells. The size 

 of the different species varies considerably, the largest frond seen 

 being 25 centimetres in diameter. All of the more perfect speci- 

 mens, whether of funnel-shaped or fan-shaped fronds, obtained 

 here, show more or less of a solid radicle by which they were 

 probably attached. 



Geological Ra7ige. — The species of fossils placed in this genus 

 are found in the Quebec, Trenton, Niagara and Hamilton for- 

 mations ; thus existing from the Upper Cambrian to the middle 

 Devonian ages. 



DiCTYONEMA RETIFORME (Hall). 



Plate 3. Figs. 1 & 2. 



(Palaeontology of New York, vol. ii.) 



" Frond circular, or expanded cyathiform in its growing state 

 (flattened in its fossil condition) ; branches thin, flat, frequently 

 bifurcating, united laterally by obliquely transverse filaments, 

 leaving oblong-quadrangular interstices ; surfaces of branches in- 

 dented, intermittingly striated in an oblique direction." 



The better preserved specimens appear to have been cup- 

 shaped, and, when flattened out, they have become sometimes 

 circular, but more frequently they have fallen on one side and 

 assumed a flabellate form, with sides largely expanded and radi- 



