GRAPTOLITES OF NEW YORK, TART 2 455 



species. The closer arrangement and somewhat different inclination of 

 the thecae indicate a differentiation here recognized as only of varietal or 

 mutational character but possibly oi specific importance. 



Dodge and Beecher have listed a "M. clintonensis" from the 

 shales of North Haven in Penobscot bay, Maine, which is possibly identical 

 with this variety. The M. priodon of Williams comes from the same 

 bed and locality as our types of the var. chapmanensis arid can, 

 therefore, be considered with certainty as belonging- to the latter. 



Monograptus beecheri Girty 



Plate 29, figure 3 



Monograptus beecheri Girty. N. Y. State Geol. 14th An. Rep't. 1895. 



p. 288; pi. 4, fig. 3-*5 

 Rast rites beecheri Freeh. Lethaea Pal. 1897. 2:116. 



Girty's elaborate description of this interesting species is : 



Stipe linear, minute, with a carination on either side. Surface marked 

 by fine longitudinal striae, which are not continuous. Denticulations about 

 the same width as the stipe, acute, distant. It is not known whether the 

 stipe is simple or branched. 



This species of Monograptus is interesting, not alone as the first exam- 

 ple of the genus reported from the Lower Helderberg rocks, but also as the 

 last known representative of this characteristic Silurian genus. Its presence 

 here is important in its bearing upon the position of the Lower Helderberg 

 group in the g-eoloo-ical scale, for similar forms have been found in the 

 earliest Devonian faunas of Germany. 



The stipe is cylindrical, sometimes tetragonally prismatic. It is hol- 

 low, with thick walls, crossed at intervals by tabulae, one for each serration, 

 which bound the zooidal habitations. On opposite sides, there are project- 

 ing ridges, or costae, the plane of the latter being at right angles to the plane 

 of the serrations. Besides the costae, there are often fine longitudinal 

 grooves or striae. The teeth are rather distant; the upper side is some- 

 times at right angles to the stipe, at others acutely inclined to it. The 

 upper surface is somewhat flattened and is pierced by circular or elliptical 

 zooidal openings, situated well toward the stipe. The under surface of the 

 teeth is sometimes flattened, sometimes rounded, the flattened examples at 

 least being provided with a median ridge. The specimens observed are all 

 fragmentary, and the nature of the sicula has not been ascertained. No 

 indications of branching have been noticed, but the zoarium ma)' be 

 bifurcated or even ramose. 



Horizon. Shaly limestone, Indian Ladder, Helderberg mountains. 



