DENDROID GEAPtOLITES OP HAMILTON, ONTARIO. 



45 



Spencer's description of this genus is as follows: 



In this genus, the frond consists of a circular disk wliich was probably cup- 

 shaped in its growing form, though fattened in a concave manner in the rock. 

 From the radicle many stipes radiate through the uoncelluliferous disk to its 

 margin, and thence in a free manner to some distance beyond. The whole 

 frond resembles a solid wheel, where the radiating spokes extend from the center 

 regularly to beyond the circumference. The branches beyond the disk are cellu- 

 liferous. The stipes have a central solid axis. The substance is highly 

 corneous, though in some places replaced by pyrites. 



Doctor Rnedemann has reviewed this genus in his monograph, to 

 which the reader is referred for comparisons between this and related 

 genera. 



Genotype. — Cydograptus rotadentatus Spencer. 



CYCLOGRAPTUS ROTADENTATUS Spencer. 



Cydograptus rotadentatus Spencer, Canadian Nat, X, 1882, p. 165, nomen 

 nudum; Trans. Acad. Sci. St. Louis, IV, 1884, pp. 565, 592, .593, pi. 6, 

 figs. 6, 6a; Bull. Mus. Univ. State Missouri, I, 1884, pp.' 15. 42, 43, pi. 6, 

 figs. 6, 6a.— Miller, North Amer. Geol. and Pal., 1889, p. 182, text 

 fig. 162.— GuRLEY, Journ. (ieol., IV, 1896, pp. 94. 309.— Ruedemann, 

 New York State Mus., Mem. 11, 1908, p. 184, pi. 2, fig. 5, 



Doctor Spencer's original description is 

 given below : 



Frond circular, with numerous stipes radiating 

 from a common center and projecting like a toothed 

 wheel beyond the margin of a noncelluliferous disk. 

 The frond was probably cup- 

 shaped when growing, with 

 the stiiies projecting upward 

 like a i"ow of spines or tent- 

 acles, but in the rock the fos- 

 sil is flattened and slightly 



convex. The stipes originate- in the center and are con- 

 nected about half their length by their continuous non- 

 celluliferous membrane. Each stipes after passing beyond 

 their solid disk divide into two branches about halfway 

 l)etween their extremities and the margin of the disk. 

 The l)ranches or stii)es are traversed I)y a central cylin- 

 drical, smooth, solid axis surrounded by their common 

 canal, which is sometimes only represented by a central 

 depression or elevation, but occasionally its form- is well 

 preserved. The rarely indicated cell openings are represented by minute oval 

 depressions in the substance. The texture is highly corneous (or replaced by 

 pyrites). 



The diameter of the frond is 2 cm., and of the disk 1 cm.; the radiating 

 branches extend half a centimeter beyond the disk, and number between 25 and 

 30, but, as each is divided, the frond is surrounded by about 60 points. The 

 branches (both through the disk and free portion) are rather over half a milli- 

 meter broad, but the terminals are scarcely more than half that thickness and 

 end in sharp points. 



Fig. 57. — Cyclogkaptl's uota- 



DENTATUS SPEXCER. COPY 



OF Spencer's figure. 



Fig. 58. — Cyclograp- 

 tus rotadentatus 

 Spencer. A large 

 specimen from the 

 Clinton group, 

 Clinton, N.Y. (Af- 

 ter Ruedemann). 



