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NEW YORK STATE MUSEUM 



other, varying from once to twice the distance between the branches, and 

 leaving quadrangular or oblong fenestrules between the same. The cellu- 

 liferous side of the frond has not been seen ; in places however where the 

 frond has been abraded the position and the frequency of the cells is dis- 

 tinctly shown. fudging from this, they are placed in a single row along the 

 middle of each branch ; there are about 13 cells in a length of 5 mm. These 

 cells seem to have an oblique upward direction, consecutive cells leaning 

 upon those in front of them, thus forming a narrow ridge or keel ; at their 

 tips the cells seem to have become more or less free, and to have developed 

 circular apertures. Noncelluliferous face striated obliquely by short, curved 

 striae simo-estin^ twisted strands. 



Frond here described, a flabellate fragment, 40 mm long and 35 mm 

 broad. From 10 to 12 branches occupy a width of 10 mm and from 10 to 



15 dissepiments occupy the same dis- 

 tance in length. The branches where 

 they are well preserved, are from 

 .5 mm to .65 mm wide. The dissepi- 

 ments vary from .1 mm to .22 mm in 

 thickness. 



The name signifies ladder-shaped. 

 This species is evidently related 

 to Dictyonema retiforme 

 Hall, differing from the same in the 

 narrower branches beino- more com- 

 pactly arranged, the dissepiments 

 likewise occurring at shorter intervals. 

 According to Prof. f. W. Spencer the 

 branches of D . r e t i f o r m e are on 

 an average about 1 mm in width. 

 The largest branches of our specimens 

 do not attain this width. 



Locality and position. Soldiers home [Dayton, 0. |, Clinton group. 

 Graptolites of this genus usually appear as black strands on the surface 

 of the rock. In this connection it is interesting to note that the cell walls 

 of Stictopora gracilis Spencer present the same appearance, 

 momentarily suggesting a graptolite. 



Remarks. Our Clinton specimen is a basal fragment or young colony; 



it has 10 to 12 branches in the space of 10 mm; its dissepiments are not 



very well preserved, but where seen but 1 mm apart, and the branches are 



in the average .5 mm wide. The thecae number 1 1-13 in to mm and are 



slender, distinctly projecting, overlap apparently about one 



Fig. 61,62,63 Dictyonema s c a 1 a r i f o r m e Foerste. 

 Fig. 61, 62 Copies of original figures. Fig. 63 Enlargement 

 (x 5) of portion of specimen from Clinton, N. V. 



hall ami possess 



