GKAPTOLITES OF NEW YORK, PART 2 121 



character of the sicular end of the rhabdosome. C. innotatus Nichol- 

 son of the British Birkhill shales is clearly a Siluric derivative of the same 

 phylum. The details of the relationships of these forms are more fully 

 given in the species descriptions. It will suffice, therefore, to state here 

 that C. put ill us and its earlier mutation eximius have most fully 

 preserved the characters of C. pungens, although the mesial spines 

 have become markedly reduced, a fact which but ill accords with the 

 general tendency to increased spinosity in the later forms of a race ; and 

 further that C. typicalis is in its sicular portion still a typical C. 

 p u t i 1 1 u s , but as the astogenetic development of its rhabdosome suggests, 

 it has under favorable conditions grown to dimensions which much contrast 

 with those of p u t i 1 1 u s . While the direct putillus race apparently 

 persisted in the Levis basin, C. typicalis comes in with the Utica 

 transgression and has hence been developed in another region. It per- 

 sisted however in the American epicontinental sea in forms which exhibit 

 a distinct tachygeny in their astogenetic development. The European 

 species C. minimus and b re vis are vicarious forms of C. putillus 

 which are most closely related to it ; likewise C. latus corresponds to our 

 C . typicalis rather than to the later derivatives of the same described 

 here from the West. 



There is also little doubt especially from the character of its sicular 

 extremity and the neastic thecae that C. scalaris, a form of world-wide 

 distribution in the Siluric is to be derived from the stock of C . putillus. 

 It appears already in the closing stages of the Champlainic (Lower Siluric) 

 in a variety (C . scalaris van miserabilis Elles & Wood) that both 

 in its dimensions and thecal characters is but little different from C. 

 putillus and quite readily can be derived from it. 



The other Climacograptidae, here described, practically all appear 

 together without any preceding forms to which they could be referred. 

 They naturally fall in several groups which are more or less related 

 to each other apparently without forming distinct phylogenetic lines. C. 

 antiquus, C. c and at us and C. parvus are closer related to each 



