GRAPTOLITES OF NEW YORK, PART 1 



565 



The feature of a loug aperturally projecting siciila we meet again as a 

 marked characteristic of the two peculiar new forms here referred to 

 Goniograptus as Gr. perflexilis and G , g e o m e t r i c u s [pl.8, fig.15 

 and 39].^ The former of these agrees in the length of the "funicle," length 

 and low inclination of theeae, slenderness of branches and relative distance 

 of their points of divergence from the principal stem, and their angles of 

 divergence so closely with Sigmagraptus praecursor, that there is 

 no doubt in my mind of the phylogenetic relationship of the two. [^See follow- 

 ing table of measurements] 





Character of theeae and 

 branches 



Length of 



branches 



of first 



order 



Number 

 of theeae 

 in 10 mm 



Inclina- 

 tion of 

 theeae 



Overlap 



Angle of 

 diverg- 

 ence of 



branches 



Width of 

 branches 



Goniograptus 





4-6 



6-7 



5° 



i-i 



80° 



A 



pe r f lexi lis 

















Sigmagraptus 



Theeae long, slender 



2.8 



8-10 



12° 



* 



90O 



.3 



praecurs or 



Slender branches 















Coenogi'aptus 





2 



8-10 



5°-16o 



i-i 



90° 



.5 



gracilis 

















S i g m a g 1' a p t u s praecursor originated from Goniograptus 

 perflexilis by the failure of the first theeae to produce two principal 

 stems each by dichotomy. The one branch developed has retained on either 

 side of the sicula the oblique position to the " funicle," the result being the 

 slightly sigmoidal curve of the principal stems. 



^ The same protrusion of the sicula beyond the point of origin of the branches 

 and its resulting conspicuity, are found also though not so typically developed in 

 another series of forms, to which Tetragraptus lentus, Didymograptus 

 filiform is and D, gracilis belong [p. 561]. Also, these forms are derived 

 from Goniograptus perflexilis. It is further very notable in a small 

 paracmic Tetragraptus [T . p y g m ae u s ; pl.l2]. 



"While this conspicuity of the sicula is partly due to the slenderness of the theeae, 

 its principal cause is the origin of the branches in all the forms at a point very near 

 the apical end of the sicula [pl.l2, tig.ll] and the abrupt diverging of the mother theeae 

 of the branches. 



