S2 NEW YORK STATE MUSEUM 



Canajoharie beds. It reaches there but 15 mm in length, and 

 appears to have possessed a rather tenuous periderm. At the Carls- 

 bad spring the specimens reach a greater size. From the geographic 

 position of these latter shales near the Glens Falls belt of Rowland 

 mills, we infer that these shales also lie near the base of the Cana- 

 joharie beds. 



From the typical Diplograptus (Mesograptus) 

 foliaceus this species is distinguished by its smaller size, nar- 

 rower sicular portion and the stronger sigmoidal curvature of the 

 ventral walls of the thecae in the obverse aspect. It does not seem, 

 however, to be nearer related to any of the other British Lower 

 Siluric Diplograpti. 



Diplograptus (Amplexograptus) macer nov. 

 PL 2, figs. 20, 21 



Description. Rhabdosome slender, 20-25 mm long with a maxi- 

 mal width of 1.5 mm, which is very gradually attained. Sicula not 

 observed. Virgella small and inconspicuous. Thecae 12-14 in 10 

 mm, about 1.5 mm long, inclined io°-i2°, overlapping about one- 

 half their length, with fairly straight or slightly sigmoidal ventral 

 and straight to slightly concave apertural margins on the reverse 

 aspect and straight vertical ventral margins and deep (one-third the 

 width of rhabdosome) apertural excavations on the obverse aspect. 



Horizon and locality. The top beds of the Canajoharie shale in 

 the Minaville section are characterized by this species. 



Remarks. D . macer is easily distinguished from the other 

 Diplograpti of the " Utica " shale by its narrow, slender form, the 

 closely arranged thecae and the very different appearance of the 

 two sides ; the rather deeply notched obverse aspect being especially 

 easy of recognition. This aspect characterizes the species as falling 

 within the subgenus Amplexograptus of Diplograptus. It would 

 seem to be a further development of that of the earlier D . 

 mohawkensis. 



This species is in many features very similar to D . (Am- 

 plexograptus) arctus Files & Wood, an earlier British 

 form of the Dicranograptus shales, and is possibly a later mutation 

 of the latter. The principal distinguishing features are the larger 

 size and the long virgella of D. arctus. 



