728 NEW YORK STATE MUSEUM 



Trigonograptus ensiformis Elles. Qaar. Jour. Geol. Soc. 1898. 54:523, 



524, %.34 

 Trigonograptus ensiformis Ruedemann, N. Y. State Paleontol. An. Rep't. 



1902. p.571 



There occur in great number on tlie shales at the dam in the Deep 

 kill section gigantic lanceolate rhabdosomes, mostly without apparent trace 

 of structure, which, as their characteristic outline and size readily sug- 

 gest, belong to Hall's Quebec species, Trigonograptus ensiformis. 



Description. Rhabdosome long, lanceolate, reaching its maximum width 

 (7 mm or more) about 20 mm from the sicular end and converging in a 

 like degree at the antisicular end. The sicular end provided with a slightly 

 geniculate, bluntly terminating, short appendage ; antisicular virgular extension 

 or nema not observed. Total length imknown ; fragments [%.3] attaining a 

 length of 80 mm and more, so that the rhabdosome may have reached a size 

 of 1 dcra. Margins in most specimens perfectly linear and unbroken. 

 Thecae indicated by the thick interthecal walls ; alternating, in contact 

 throughout their whole length, numbering 10 to 11 in the sicular portion 

 and, mostly, only 8 within the space of 10 mm in the mature portions. 

 The apertures, which are rarely well shown [iig.7, 9], are subquadratic, 

 lying in one line and obliquely to the axis of the thecae ; they are with- 

 out any apertural appendages. The thecae form an angle of about 45° with 

 the axis of the rhabdosome. Along the latter, in somewhat macerated 

 specimens a perfectly straight, stout virgula is seen to pass. The test does 

 not show any traces of reticulation, but is smooth and thick, and often 

 bordered by longitudinal thickened lines, apparently formed by the confluence 

 of the latei'al apertural margins. 



Position and localities. In graptolite bed 6 of the Deep kill section, 

 belonging to the zone with D i p 1 o g r a p t u s d e n t a t u s , The species 

 has been also observed, though less frequently and in smaller specimens, in the 

 base of this horizon at Mt Moreno. 



Hall's types came from the Quebec group at Point Levis. According to 

 Grurley, it occurs there in the upper zone, with Diplograptus 



