GKAI'TOLITES OF NEW YOUK, PART 1 741 



Dawsonia tridens Gurley 



Plate 17, Hgure 18-20 



Dawsonia tridens Gurley. Jour. Geol. 1896. 4:88, pl.5, fig.5 

 Dawsonia tridens Ruedemann. N. Y. State Paleontol. An. Rep't. 1902. 

 p.556 



DesGi'iption. Rhabdosorae shortly and asymmetrically fusiform in out- 

 line ; about 3 mm long (3.4 mm maximal length observed), 1.1mm wide, drawn 

 out at both extremities into blunt mucros. A median groove, which becomes 

 most distinct at the athecal extremity, connects the mucros. On one side 

 there are two or three oblique incisions which produce acute denticles of the 

 appearance of thecae. Otlier side more convex, with entire margin. Sub- 

 stance chitinous (?), thin. 



Position and localities. Common at the Deep kill in graptolite beds 1 

 and 2 of the Tetragraptus horizon. Gurley obtained his types from the same 

 horizon at Point Levis. 



Rettmrlis. Our material agrees in most particulars with the description 

 and figure given by Dr Gurley. We Avere, however, unable to discern the 

 " pustules " observed by him at the inner ends of the incisions ; but noticed 

 sometimes a Avidening of the incisions at this place [iig.lSJ. The groove, 

 described !)y the same author, as occurring at the blunter extremity, crosses 

 our specimens longitudinally. As Gurley remarks, this species resembles in 

 outline and size most closely D. acuminata Nicholson. The latter, 

 however, has ojie extremity rounded and can by this feature be readily 

 distinguished. 



Dawsonia monodon Gurley 



Plate 17, figure 21-26 



Dawsonia monodon Gurley. Jour. Geol. 1896. 4:88, pl.5, fig.4 

 Dawsonia monodon Ruedemann. N. Y. State Paleontol. An. Rep't. 1902. 

 p.554, 556 



Description. Rhabdosome elongate rhomboidal in outline; about 10mm 

 long and 3 ram wide ; of the two extremities of the major axis one (proximal 

 one?) rounded, the other acutely tapering; the two lateral extremities 

 extended into shorter, downAvardly directed mucros. The acutely tapering 



