462 NEW YORK STATE MUSEUM 



camera drawing and all the others presented scalariform aspects and nearly 

 smooth margins. There is little doubt that this mode of preservation is 

 also to a great extent due to the curvature of the branches which is such 

 that they rarely come to rest upon their lateral faces. 



Family retioutidae Lapworth 



RETIOGRAPTUS Hall 



A sketch of the history of this genus has been given in Memoir 7 

 [p. 732] and one of the three species which have been referred to Retio- 

 graptus (R. tentaculatus) has been described more fully from mate- 

 rial obtained in the Deepkill shale. In the present publication the two 

 remaining species (R. e u char is and R. geinitzianus) are rede- 

 scribed, the New York rocks having furnished specimens which much sur- 

 pass the types in completeness of preservation. This new material has 

 shown that the first named of the two species was originally misunderstood 

 in regard to the arrangement of the thecae which is described as being rec- 

 tangular while in fact, it is as in Diplograptus, and the exterior aspect of the 

 thecae is typically diplograptid. We have for reasons given before, placed 

 the form under Glossograptus. It has also been found that in the other 

 species, R. geinitzianus, the structure of the skeleton, especially the 

 character of the axes, is most suggestive of Glossograptus. No correspond- 

 ing structure has as yet been observed in the genotype of Retiograptus, 

 R. tentaculatus, but the great external similarity of the latter to R. 

 geinitzianus suggests that it may possess it. In that case all the forms 

 here mentioned will be finally associated in a subdivision of Glossograptus. 

 With this view in mind we have, for the present, left R . geinitzianus 

 in its original place. 



The citation of the rectangular arrangement of the thecae, as one oi 

 the principal characters of the genus is, as here shown, based on misconcep- 

 tion. In G. (?) eu char is a certain preservation facies produces the 

 aspect and in the other two species the horizontal parietal ledges are 

 responsible for the apparent presence of horizontal thecal walls. 



