GRAPTOLITES OF NEW YORK, I'AKT 1 659 



Description. Small subcircular primary disk and very thin filiform nema. 

 Rliabdosome of small size (usual length about 12 mm); forming a broad 

 oval in younger, a more elongate truncate oval in older specimens ; consisting 

 of four relatively wide branches (1 .6 mm at their origin, rapidly attaining a 

 width of 2.5 mm and diminishing again toward the extremity), which in 

 most specimens are straight or slightly concavely curved on the dorsal side 

 and present a stronger convex outline on the frontal side. 



Sicula about 2 . 1 mm long, stout. Branches of the first order monothecal, 

 each 1 . 1 mm long. Those of the second order short (rarely exceeding 13 mm 

 in length), in typical specimens flexed, curving upward and inward. Thecae 



Fig. 58 Tetragraptus simillB Hall »p. Two specimens, in which 

 only the branches of one side are retained ; in a the branches are seen from 

 the outside ; in b from the inside of the rliabdosome. Deep kill. x5.25 



numbering 10 to 14 in the space of 10 mm, gradually ascending (initial angle 

 about 50°), but curving outward in their distal parts (angle 60° to 70°), 

 widening toward the aperture, four times as long as wide; in contact four 

 fifths of their length. Apertural and external margins slightly concave, both 

 forming a characteristic recurving, mucronate apertural denticle. 



Position and localities. Occurring in great profusion in the Tetragraptus 

 bed of the Deep kill, specially graptolite bed 2, still met in scarce and depau- 

 perated specimens in graptolite bed 3, which represents the lower part of the 

 zone with Didymograptus bifidus. 



This species, which in mature representatives, is very readily recognized 

 by the curved, relatively broad branches and the curved apertural denticles, 

 is evidently a form of vast distribution. It was originally described by Hall 

 as occurring in great multitudes in the Quebec shales at Point Levis, where 



