•1 



(iRArTOLlTHS OF MOW YOUK, I'AU'r 1 (>T7 



the smaller number of tliecae in a unit of length and the general absence of 

 curvature in tlie branches of D. pat ul u s as distinctive characters. Their 

 specimens of the latter species have a looser arrangement than ours (9 to 10 

 in 10 mm), while the thecae in the drawings [p.l4] d(^ not exhibit the curva- 

 ture and inclination described by Hall as charactei'istic of that species. 



These facts indicate that there is a 

 considerable number of varieties grouping 

 themselves around and between the typical 

 forms of D . p a t u 1 u s and D . n i t i d u s . 



We have observed a primary disk Haif,sp.''Fra?men\o\^d1stai pinion or'Ua^ 



-^ , Deep kill. X5.25 



which in the specimen figured [fig. 9J is 



subcircular, fairly well outlined, has a diameter of about 12 mm and though 

 sho-\ving but a trace of carbonaceous substance, is distinctly set oif from the 

 surrounding surface by its smoothness and depressed margin. Like the 

 primary disks of other forms, it possesses in the center a small, somewhat 

 more projecting circular portion. The apex of the sicula lies upon the apex 

 of this projection and ^vas hence evidently fastened to the disk either by a 

 very short nema or without the intercalation of one. Since in hundreds of 

 otherwise perfect specimens of D . p a t u 1 u s the sicula shows no trace of 

 a nema, I feel satisfied that this species w^as closely attached to the primary 

 disk, and not suspended by means of a long nema as D. (g i b b e r u 1 u s) 

 c a d u c e u s . 



Didymograptus similis Hall sp. 



Plate U, fig-ures 25-29 



Didymograptus similis Hall. Canacliau Organic Remains decade 2. 1865. 



p.78, pl.2, fig.1-5 

 Didymograptus similis Gurley. Jour. Geol. 1896. 4:295 

 Didymograptus similis Ruedemanu. N. Y. State Paleontol. An. Rep't. 1902. 



p.566, 567 



Description. Nema and primary disk not observed. Sicula small and 

 inconspicuous, about 1.8 mm long. Branches diverging at 180°, maximal 

 length attained unknown (longest fragment ob3erved 45 ram); widening 



