126 NEW YORK STATE MUSEUM 



loid stage of development when it is first observed in the third Deepkill 

 zone. 



We believe that the just mentioned characters of the periderm also 

 serve to indicate a closer relationship between Cryptograptus and Lasio- 

 graptus. It is in this connection important to note that also the general 

 aspect of the rhabdosomes of the two genera, as well as that of the thecae 

 show many points of agreement, as the great difference in width between 

 the frontal and lateral aspects, the lax appearance of the rhabdosome in the 

 lateral aspect and the arcuate form of the thecae with a short perpendicular 

 distal outer wall. Cryptograptus appears long before Lasiograptus in the 

 third Deepkill zone with C. antennarius and continues into and 

 through the hemera of Lasiograptus with a species (C . tricornis) but 

 little different from and clearly a descendant of the former. 



The Deepkill form still possesses such strong climacograptoid features 

 that in Memoir 7 we have referred it — with doubt — to that genus and 

 consider it entirely probable that it took its origin from an early climaco- 

 graptid stock. There is good reason to infer that Lasiograptus was derived 

 independently from Cryptograptus from the same stock. As both Lasio- 

 graptus and Cryptograptus also still retain distinct diplograptid features, 

 it is entirely proper to further infer their derivation from primitive 

 Climacograpti still little differentiated from Diplograptus. 



Since the reticulation of the periderm itself has not yet been observed 

 in Cryptograptus, we have here not placed this genus with the Retiolitidae 

 where it eventually may find its place, but have indicated its transitional 

 character to the latter family by its terminal position in the Diplograptidae. 



