750 NEW YORK STATE MUSEUM 



PLATE 2 



Grenus staurograptus Emmons 

 Staurograptus dichotomus Emmons 



Page 614 



1-13 Growth stages 



1 Sicula with nema and primary disk ; the latter shaded much too dark in 



proportion to the thickness of its test. x5 



2 Sicula showing aperture and fragment of primary disk. x5 



3 Sicula with budding first theca. x5 



4 Sicula with long nema, matured first and budding second theca. x5 



5 Young rhabdosome with fragmentary primary disk and three thecae. x5 



6 Young rhabdosome in which the coenosarcal cavities have been filled with 



pyrite and are plastically preserved. The point of gemmation of the 

 first and second theca and the formation of the four secondary branches 

 by bifurcation are distinctly shown. The latter takes place so close to 

 the sicula that apparently four branches spring from the latter 

 [see fig.7-10]. x5 



7 Somewhat obliquely compressed young rhabdosome which shows the first 



bifurcation of a secondary branch and the succeeding thecae of the 

 branches. x5 



8 Frontal view (or rhabdosome, seeu from below) of a somewhat younger 



stage showing the aperture of the sicula in the center. x5 



9 Like view of an older growth stage in which three of the four secondary 



branches have divided by dichotomy. x5 



10 Like view of a still more advanced stage in which all four secondary 



branches have again become bifurcated and one begins to form branches 

 of the fourth order. The form described by Emmons as Stauro- 

 graptus dichotomus was a growth stage but slightly les^^3 

 advanced than this. x5 



1 1 Same view of a stage which exhibits an unequal development of the four 



secondary branches. x5 



