688 XEAV YOKK STATE MUSEUM 



Didymograptus tbrnquisti sp. no v. 



Plate 13, figures 6, 7 



Description. Primar)' disk niiknown ; nema present. Sicula small (1 . 2 

 mm). The point of origin of the first theca has not been distinctly observed. 

 The branches diverge near the apertnral end of the sicula, are nearly horizontal, 

 gently curved, attaining their full width (1.1mm) near the ]3roxiinal part 

 and maintaining it. Thecae numbering 8 in 10 mm, inclined at an angle of 

 about 20", tliree times as long as wide, in contact about one third of their 

 length. Outer and apei'tural margins straight, the latter normal on direction 

 of axis of theca. 



Position and locality. In graptolite bed 3 (zone of D . b i f i d u s) asso- 

 ciated with Gr oniogr aptu s geometric us, Tetragraptus pen- 

 dens, D . b i f i d u s and D. si mills. 



JRemarhs. Only one specimen of this species has been observed. Its 

 principal characters, viz the loose arrangement and low inclination of the 

 thecae and the small amount of oveilap, distinguish it from other forms 

 except D. affinis Nich., which however has much narrower branches 

 and a shorter sicula. From the similar D . n i c h o 1 s o n i var, planus, 

 which occurs in the underlying bed, it differs by the smaller number of 

 thecae in a unit length. 



Didymograptus spinosus sp. nov. 



Plate 14, figures 30-32 



Description. Primar}^ disk and nema not observed. Sicula small and 

 little conspicuous (.9 mm). First thecae diverging suborally. Branches 

 moderately deflexed, their angle of divergence about 120°; very thin at the 

 beginning (not .8 mm wide), but widening rather rapidly Avithin 10 mm to 1 

 mm. Mature length and Avidth of branches unknown ; the longest branch 

 observed attains a length of 16 mm. Thecae numbering 12 in 10mm; nar- 

 row, four times as long as wide in the proximal and three times as long as 

 yndid in the more distal j^arts of the rhabdosome ; inclined at 20"^ ; in contact 



