404 NEW YORK STATE MUSEUM 



some Leptograptuslike form, by means of an alteration of the sigmoid 

 curvature of the theca into a double geniculation and the coalescence of the 

 free uniserial arms by their dorsal sides, the smaller or greater number of 

 alternating pairs of thecae and the corresponding earlier or later develop- 

 ment of the longitudinal septum would appear to be well able to give some 

 clues as to the stage of development of a particular species, the smaller 

 number of alternating thecae indicating a lower stage. It then also 

 becomes impossible to derive Climacograptus from Diplograptus, the latter 

 genus according to this criterion and in this regard being more advanced 

 than Climacograptus by the extension of the biserial chamber on the whole 

 or the greater part of the rhabdosome. 



Synrhabdosomes of Climacograptus have not yet been found, but it is 

 hardly to be doubted that as in Diplograptus and Lasiograptus, also in this 

 genus the rhabdosomes were combined into colonies of a higher order. 

 The expansions of the nemacaulus observed so frequently in certain species 

 of Climacograptus can not be considered as part of the central organs, for 

 the nemacaulus is seen in some cases to proceed beyond them. Their 

 structure and function have been discussed on page 88. 



The first attempt at subdividing the genus, of which I am aware, has 

 been made by Freeh, who, seeing in the two lateral spines of the sicular 

 end ' functionally important organs, makes them the principal criterion of 

 distinction, thereby separating C . b i c o r n i s and C . antennarius 

 from the rest of the congeners. The latter form is a true Cryptograptus, 

 and to be removed from this association, thus leaving C . b i c o r n i s alone 

 in the first group. And its spines can be hardly given more than varietal 

 rank as diagnostic characters; for many of the other congeners (as C. 

 p a r v u s , C . modestus, C . caudatus, C . a n t i q u u s ) possess 

 small lateral spines; in one species (C. typical is) the typical speci- 

 mens seem to lack them while a mutation is furnished with them ; and also 



1 They are called " Sicularstacheln " by him, which term is not appropriate in the case 

 of Climacograptus bi corn is, as the two lateral spines are borne by the first two 

 thecae and not by the sicula, from which the third spine, the virgella, proceeds. 



