732 NEW TOBK STATE MUSEUM 



EUes, and again to Cliniacograptxis by Freeh, who does not recognize 

 the genus Cryptograptns. An inspection of the numerous specimens from 

 the Deep kill explains this uncertainty ; for, while the outlines of the rhabdo- 

 soraes are shai-ply defined, they are nearly always uninternipted and straight, 

 and the surfaces of the rhabdosomes are perfectly smooth. The apertures 

 of but one specimen [fig,22] could be seen fairly well in the frontal aspect, 

 and the thecae of another in their profile view [fig.24]. From these 

 observations I infer that the thecae had the same position as in Cliraaco- 

 graptus. Moreover, the strong development of the distal spines is a char- 

 acter most developed in the later species of Climacograptus, and, hence, to 

 some extent indicative of this genus. Yet, in its habit this form is by no 

 means a typical Climacograptus, and for this reason it is here referred 

 with doubt to that genus. 



Lapworth expressed his belief that this species may belong to his 

 genus Cryptograptus ; and the general form of the rhabdosome and the three 

 strong distal spines are characters certainly very similar to those of the 

 genotype Cryptograptus tricornis; but the thecae of that form are 

 described and figured as inclined, and so are those of Cryptograptus 

 hopkinsoni, which, in the profile view, remind one strongly of those 

 of Diplograptus dentatus. 



The perpendicularly projecting spinules, observable according to Hall 

 along the margins of the rhabdosomes in some specimens, have not been 

 noticed in the Deep kill material. 



RETIOGRAPTUS Hall. 1865 



Hall separated the genus Retiograptus from Barrande's genus Retio- 

 lites, making the species described here the type of the new genus and 

 stating that the three species which he refers to it " are nearly related to 

 Retiolites ; but the texture of the specimens examined, and the ai'range- 

 ment of the parts, differ so much from authentic specimens of Retiolites 

 geinitzianus, that I have separated them under the above designation." 

 The author of Retiograptus concedes that the three species united under 

 this generic designation present some impoi-tant points of difference, 



