GRAPTOLITES OF NEW YORK, PART 1 679 



alike. D. suecicus and D . d e c e n s are hardly to be distinguished fi'om 

 each other. Professor Tornquist, the author of the latter species, doubts 

 himself ^vhether they are really distinct and mentions the apparent 

 occurrence of transitional forms. The facts, that D. suecicus has over- 

 lapping thecae Avhich widen more toward the aperture, and that their outer 

 margins are distinctly curved and free for but one third, are cited as affording 

 distinctive characters. If we accept these differences as of specific value, D . 

 suecicus will have to be regarded either as a vicarious form of D . 

 similis or, 1 believe, as really identical with the latter and D. decens as 

 a very closely related form. Tullberg held his D . suecicus to be nearly 

 related to D. nitidus Hall. The latter differs, however, essentially in the 

 rate of widening of the branches and specially in the much closer arrange- 

 ment of the thecae. 



D. suecicus occurs, according to Tornquist, abundantly in the third 

 zone of the PhylloTetragraptus beds (zone with Ph3^11ograptus 

 d e n s u s), and more sparingly in the second zone (zone with D. balticus). 

 Hence it holds there about the same level in the lower graptolite shales as 

 D. similis in America and is a member of a corresponding faunule. 



Didymograptus gracilis Tornquist 



Plate 14, figures 15-21 



Didymograptus gracilis Tornquist. Undersokriingar ofver Siljansomradets 



Graptoliter I (Aftryck ur Lunds Univ. Arsskrift. Tom. 26). 1891. p.l7, pl.l, 



fig.9-12 

 Didymograptus gracilis Holm. Geol. Foren. Stockh. Forh. Bd 17, H3, 1895. 



pl-l,fig.7,8 

 Didym ograptu s gracilis Elles. Quar. Jour. Geol. Soc. 1895. 54:506 

 Didymograptus gracilis Elles & Wood. Monogr. Brit. Grapt. ptl. 1901. 



p.2i, pl.2, fig.2 

 Didymograptus (Leptograptu8)sp. nov. Rnedemann. N. Y. State Paleontol. 



An. Rep. 1902. p.589, fig.l7 

 Non Graptolites (Didymograptus) gracilis McCoy. Geol. Sur. Victoria. 



Prodr. Pal. Victoria, decade 2. 1875. p.35 



