GUAPTOLITES OF NEW YORK, PART 1 



661 



evidence of the derivation of T. taraxacum from a form with the 

 thecal characters of B. lapworthi.^ 



Bryograptus lapworthi can be considered as having descended 

 through unknown intermediate forms from Staurograptus dicho- 

 t o m u s var. a p e r t u s with some degree of certainty, springing from the 

 fact that the character and arrangement of the thecae in the two species fairly 

 agree (number of thecae 11-13 in 10mm in S. dichotomus var. 

 a p e r t u s ; angle of inclination 25° ; overlap \). 



(8) A series with strong diagnostic characters is that leading from 

 Goniograptus perflexilis through a peculiar flexuous, four 

 branched form, Tetragraptus lentus, to Didymograptas 

 filiformis and D. gracilis. 



The specific names of all four species express the thin, flexuous 

 character of the branches, which is due to the extreme length (3 mm) and 

 narrowness of the thecae, as well as to their small overlap (one fourth) and 

 loose arrangement (6-10 in the space of 10 mm). 



A peculiar character which these forms have in common vrith the 

 Coenograptus series, also to be derived from Goniograptus per- 

 flexilis, is the origin of the branches about midway of the sicula. 



* The change in the character of the thecae of T. taraxacum has been discussed 

 by the writer in another connection [1902, p.589]. 



