GRAPTOLITES OF NEW YORK, PART 1 



565 



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

 marked characteristic of the two peculiar new forms here referred to 

 Goniograptus as G. perflexilis and G. geometricus [pl.8, fig.15 

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

 and low inclination of thecae, slenderaess 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. ISee follow- 

 ing table of measurements] 



Sigmagraptus praecursor originated from Goniograptus 

 perflexilis by the failure of the first thecae 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. pygmaeus; pl.l2]. 



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

 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, figll] and the abrupt diverging of the mother thecae 

 of the branches. 



