406 NEW YORK STATE MUSEUM 



calis [see fig. 2>77^ as Nicholson correctly observed and judging from 

 his drawing and description also thecae similar to the earlier (neastic) 

 thecae of C . t y p i c a 1 i s . We would also derive C . s c a 1 a r i s from 

 this group. 



Another natural group among our species of Climacograptus is formed 

 by C. parvus, C. modest us and C. s c h a r e n b e r gi. It is 

 rather well characterized in the compressed condition, by the nearly uniform 

 width of the rhabdosome, square-shaped free distal parts of the thecae, the 

 deep, narrow, horizontal apertural excavations and the prevailing presence 

 of lateral spines at the sicular end, and in the plastic form by the more or 

 less zigzagged shape of the sutural groove and the corresponding consider- 

 able divergence of the directions taken by the different parts of the theca. 

 C. scharenbergi is the oldest and most typical form of this group. 

 C . b i c o r n i s with its extreme development of the lateral spines and C . 

 caudatus with an equally extreme development of the virgella stand 

 apart of this group by their gradually widening rhabdosomes, the wide, but 

 shallow apertural excavations and the oblique direction of the free distal 

 parts of the thecae. Both of these may be connected with C . antiquus 

 which is older as well as similar and, possessing both long lateral spines 

 and a long virgella, would seem well fitted to have given rise to these two 

 species. 



The range of the genus corresponds in our region approximately to 

 that found in Europe. There is one species, C. pungens, found in 

 the third Deepkill zone (with Dipl. dentatus) ; six are known from the 

 Normanskill shale, two of which persist (mutationally differentiated) into 

 the Utica and Lorraine beds; one is found in the beds intervening between 

 the Normanskill and typical Utica beds (zone of Dipl. amplexicaulis) ; 

 another is restricted to the Utica shale and one is here described from the 

 Clinton beds of Maine. 



