'58 



NEW YORK STATE MUSEUM 



about i mm. At the same time these are not so frequently visible as to 

 warrant an assertion that this minimal distance is the usual one, and the 

 material, slightly worn, as it is, leaves me in some doubt on the point. In 

 several places a few thecae can be seen, apparently set about 50 in 25 mm. 

 The branches near the base are thicker (0.6 mm) in number about 25 in 

 25 mm. 



Position and localities. Hall stated that this species occurs only in the 

 shale at Lockport, N. Y. Newer collections by the State Museum show 

 that, in some outcrops of the Rochester shale, it is a very common form, as 



for instance at Middleport, N. Y., where it is 

 associated with Palaeodictyota a n a s- 

 tomatica. Spencer has also recorded it 

 from the Lockport limestone at Hamilton, 

 Ontario and Rominger cites it from the 

 Manistique river, Michigan. 



Remarks. Some excellently preserved 



material, obtained at Middleport, allows us to 



. add the following data to the above given 



Fragments showing different aspects of the - , . _, 1 111 



thecae; figure 66 also dissepiments. Original deSCri ptlOll. 1 lie rhabdOSOlTie WaS CVathlform, 



of figure 66 is from the Niagaran limestone at * < ' 



Hamilton, Out.; those of the others are from 1 • . I" 1 , • 1 



the Rochester shale at Middiepon, x.y. x 5 expanding at a medium rate and attained con- 

 siderable size, one fragment having a length of 14 cm. In one (young ?) 

 specimen a short basal stem (2 mm long) and a small adhesion disk are 

 seen. The thecae are not as closely arranged as Gurley concluded, they 

 number but 13-14 in 10 mm; they are quite prominent, their angle of 

 divergence being 30°, and overlap almost one third their length, their 

 ventral margin is straight, the apertural margin very concave, the denticle 

 acute and ending;' in a mucro. 



Dictyonema polymorphum Gurley ms 



Plate 2, figure 3; plate 3, figures 4, 5, 6 



Dictyonema tenellum Spencer. Acad. Sci. St Louis. Trans. 1SS4. 



fig. 13 (not the description, p. 576) 

 Dictyonema tenellum Spencer. Mus. Univ. State Mo. Bui. 1SS4. 



fig 13 (not the description, p.26) 



v. 4. pl. 1, 



v. 1, pl. 1, 



