578 NEW YORK STATE MUSEUM 



DESCKIPTIONS OF GRAPTOLITES 



Order 1 DENDROIDEA Nicliolson 

 Family dendrogra.f'Tida.e Roemer 



DENDROGRAPTUS Hall. 1865 



The genus Dendrograptus was erected by Hall for forms with a strong 

 main stem and a broad, spreading, sbrublike, variously ramifying frond. 

 The thecae are described as quite distinct and angular in some (the type 

 species of the genus, D. hallianus Prout), of obscure form in others, 

 while in still others they are shown only as round or elliptic pits or 

 pustules. 



Wiman [1895, 1900] has been able to isolate and investigate under the 

 microscope four different forms which he refers to this genus. These pos- 

 sessed an internal structure similar to that in Dictyonema, viz a composition 

 of three different kinds of thecal tubes, representing, according to Wiman, 

 nourishing, and budding individuals and gonangia [p. 5 9 2]. In those three 

 of these four species which also from their external characters would be 

 readily placed with Dendrograptus, all branches are simple, i e. consist of but 

 one series of individuals. 



There is no doubt that eventually the internal structure will furnish 

 the means of recognizing the phylogenetic relations of the forms united 

 under Dendrograptus and of procuring thereby the criteria for a sharp and 

 natural division or dissolution of the genus, which clearly contains very 

 different elements. It has evidently been made the receptacle of all arbori- 

 form graptolites ; and the fact of the great difference of the thecal apertures 

 mentioned by Hall, in the original description of the genus, indicates already 

 its heterogeneous character. We see at present no other way than referring 

 a species like the D. ? succulentus of this paper to this genus, as 

 there is no other designation extant for similarly constructed forms, and it 

 would be unwise to undertake the dissolution of the genus by external 

 characters, at a time when it becomes probable that the internal characters 

 will furnish safer criteria for such a proceeding. 



