GRAPTOLITES OF NEW YORK, PART 1 727 



graptidae on account of their origin by alternate budding ; and the axis 

 was originally described as having a zigzag form in T . 1 a n c e o 1 a t u s , 

 while that of T . e n s i f o r m i s has always been known to be straight or 

 but slightly undulating [pi. 17, fig. 4]. Nicholson's observation of a zigzag 

 axis in the type species appears not to be verified by Elles, who, after 

 inspection of that author's type material, cites the greater inclination of 

 the th^ecae in T . 1 a n c e o 1 a t u s as the only difference between the two 

 species of the genus. 



Thus the indentate margin remains the only distinctive character of 

 the genus. This straight, undivided margin is due to a peculiar obliquity 

 of the apertures to the axis of the thecae, as some of our specimens clearly 

 show [fig. 9], the a]_'>ertural angles of the thecae being approximately equal to 

 their inclination angles, both forming thus alternating angles between 

 parallels. 



The oblique position of the apertures is also the only difference I am aware 

 of, between this genus and Diplograptus ; the former should, hence, probably 

 be regarded as representing an aberrant branch of the Diplograptidae, one of 

 the variety of forms \vhich are characteristic of the first outburst of that 

 family, and which soon disappeai" again. Trigonograptus can not be con- 

 sidered a climacograptid, though where, oy maceration or compression, the 

 thecae have slightly separated, the appearance of a climacograptid is some- 

 times produced. 



Trigonograptus ensiformis Hall sp, 



Plate 17, figures 1-9 



Retiolites ensiformis Hall. Geol. Sur. Can. decade 2. 1865. p.li4ff, 



pl.14:, fig.1-5 

 Trigonograptus ensiformis Hopkinson & Lap worth. Qaar. Jour. Geol. 



Soc. 1875. 31:659ff, pl34, %.8a-c 

 Trigonograptus ensiformis Ami. Geol. Sur. Can. Rep't, ser. 2. 1889. 



V.3, pt2, p.ll7k 

 Trigonograptus ensiformis Nicholson. Geol. Mag. ser. 3. 1890. 7:340, 



341, fig.l, 2 

 Trigonograptus ensiformis Gurley. Jour. Geol, 1896. 4:299 



