GRAPTOLITES OF NEW YORK, PART 2 211 



simple indentations on the surface, and sometimes distinctly angular, with 

 the denticles conspicuous ; " adding that " in some specimens the cellules 

 are indicated by prominent pustulelike elevations, arranged along the center 

 or in subalternate order on one face of the branch." Corresponding to the 

 wide compass of this description a great variety of forms has, in the course 

 of time, been brought under Dendrograptus. We have already in Memoir 

 7 pointed out that it has become the receptacle of all arboriform graptolites 

 and that the fact of the great difference of the thecal apertures mentioned 

 by Hall, Indicates its heterogeneous character. 



We have now before us a form (M . tenuiraraosus) from the 

 upper graptolitiferous beds which while originally described as a Dendro- 

 graptus and also properly referable to that genus as originally diagnosed, 

 shows a structure totally different from that of the genotype of Dendro- 

 graptus (D. hall i an us Prout) and at the same time is representative 

 in its general habitus of a large group of the forms brought under 

 Dendrograptus. 



Dendrograptus h alii an us has distinct "denticles," i.e. pro- 

 jecting thecae of the appearance of those of Dictyonema and Wiman has 

 shown that also the internal structure of similar denticulate Swedish forms 

 is as complex as that of Dictyonema. D. tenuiraraosus, however, 

 while arborescent in its habit, has smooth whiplike branches, which as 

 Walcott has correctly observed, in the great number of specimens found in 

 the Utica shale of Holland Patent, N. Y., exhibit nothing but a row of 

 obscure pits, apparently the thecal apertures. The same is the case with 

 the associated D . simplex and with other species of Dendrograptus. 

 Dr Ulrich, however, has obtained material of a Dendrograptus in the Eden 

 shale in Kentucky which he has, as I believe, correctly referred to D . 

 tenuiraraosus and which in beautiful preservation exhibits additional 

 features \see postea\ thereby revealing a structure entirely different from that 

 of D. hallianus and the forms investigated by Wiman. We believe 

 therefore in the necessity of separating these forms generically from Dendro- 

 graptus and in restricting the latter genus to species with distinct denticles. 



