(580 NEW YOUK STATE MUSEUM 



lu the base of gruptolite bed 3, the lowest outcrop of the zone with D. 

 b i f i d u s, several specimens of an extremely delicate Didymograptus were 

 collected. These differ in no way from a species first noticed in Sweden. 

 We give here a translation of the original description of the species. 



From an almost uniformly thick sicula of 1 mm in length the two branches 

 diverge at distinctly different hights, the one almost from the middle, the other 

 from the upper end. Above these points of divergence the aperture of the 

 sicula runs o1)li(piely upward, so that it projects Avith a triangular tooth 

 beyond the upper braucli. The branches are of uniform width, .2 to .3 mm 

 wide, and diverge almost at right angles from the sicula, but are irregularly 

 bent in their continuation. AVithin a space of 10 mm 6 to 8 thecae are con- 

 tained. These are long and narrow, with the peiiderm compressed, widening 

 toward the aperture to about double the width. The outer wall of the thecae 

 is slightly concave, sometimes almost sti'aight ; it forms a veiy acute angle 

 with the dorsal margin. The apertural margin is perjiendicular on the dorsal 

 margin. Sometimes I believe I have seen a short internal canal. The length 

 of the branches is unknown, but was cei-tainly 15 to 20 mm and probably 

 more. 



Occurs in Phyllograptus shale at Skattungbyn. Fragments of branches 

 are very common upon certain shales. 



To this careful description we need only to add in way of enlargement 

 that the branches are horizontal in their proximal part for the length of about 

 three thecae and then mostly become gently reclined, a feature also apparent 

 in Tornquist's drawings, or become fiaccid ; that the thecae are three to eight 

 times as long as Avide, their slenderness increasing distally, where the greater 

 part of the thecae appears as a very gradually \videning, hair-fine tube ; and 

 that the angle of inclination of the thecae is not more than 5° in the mature 

 portion of the branches. 



Position and localities. This species is not infrequent in graptolite bed 3 

 (the base of zone with D. b 1 f i d u s ^), where it is associated with Gonio- 

 g r a p t u s g e o m e t r i c 11 s and D. nan u s, and it has also been found to 

 occur still rarely in the beds at Mt Moreno, which contain a fauna transitional 

 from this zone to that with Diplograptus dentatus. Tornquist 



* In the Report of the State Paleontologist for 1901, p.556, this form lias, aa 

 D. (L e p t o g r a p t u s ) sp., been erroueously cited from graptolite bed 2. 



