184 NEW YORK STATE MUSEUM 



that the thecae seem to be very indistinct. This, however, is probably 

 only an apparent difference, and due to the fact that the thecae are, as 

 also in Discograptus, all turned inward on the branches, and the latter 

 exhibit only their frontal sides in the compressed condition. 



Cyclograptus rotadentatus Spencer 



Plate 2, figure 5 



Cyclograptus rotadentatus Spencer. Can. Nat. 1882. 10:165 

 Cyclograptus rotadentatus Spencer. Acad. Sci. St Louis. Trans. 1884. 4:565, 



59 2 > 593 ; pl- 6 , fl g- 6 , 6il 

 Cyclograptus rotadentatus Spencer. Mus. Univ. State Mo. Bui. 1884. 1 : 15, 



42, 43 ; pi- 6 , fig- 6 , 6a 



Cyclograptus rotadentatus Miller. N, Am. Geol. &: Pal. 1889. p. 182, fig. 162 

 Cyclograptus rotadentatus Gurley. Jour. Geol. 1896/ 4:94,309 



Spencer's description of this form reads : 



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 stipes 

 projecting upwards like a row of spines or of tentacles, but in the rock the 

 fossil is flattened and slightly convex. The stipes originate in the center, 

 and are connected about half their length by their continuous noncellu- 

 liferous membrane. Each stipe after passing beyond their solid disk 

 divide into two branches about halfway between their extremities and the 

 margin of the disk. The branches or stipes are traversed by a central 

 cylindrical, smooth, solid axis surrounded by their common canal, which is 

 sometimes only represented by a central depression or elevation, but occa- 

 sionally 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 millimeter broad, but the terminals are scarcely more than half that thick- 

 ness and vnd in sharp points. 



Formation and locality. This perfect little species was found in the 

 dolomite of the Niagara formation proper, near the base ot the series, at 

 the quarry just west of the "Jolly-cut road," at 1 lamilton, Ontario. 



