GRAPTOLITES OF NEW YOKK. PART 1 



541 



layer and the columnar layer [see fig. 13, 14]. The last two are distinctly 

 composed of calcite crystals. As these two zones are correlatives in theii- 

 width — the one is in some places entirely replaced by the other — and 

 as they are separated b}' a jagged line, corresponding to the sections of crys- 

 tals, it is to 1)6 inferred that they result from a single deposit of fibrous 

 calcite crystals, which, being slightly curved, show in the angular zone 

 their sections and in the columnar zone theii* lateral faces. Bands of 

 brown pigment appear at irregular intervals in the angular zone. No traces 



Fig. U 



Fig:. 13, U Dichoprraptiis sp. Thin sections through walls of pyritized 

 specimens. Deep kill. X215 



of an exterior or interior epidermis have been observed in any of the sections, 

 but it is quite possible that these, if present, are, on account of their thinness, 

 entirely concealed by the pyrite matrix. 



It can be considered however as established by Perner's and Wiman's 

 observations that there existed an "epidermis" besides the principal black 

 wall. In other forms, as in numerous species of Lasiograptus, which the 

 writer has collected in the Trenton graptolite beds, and which will be 

 described in the next memoir, the thin epidermal layer and the principal one, 

 which there is dissolved into a network of fibers, can be readily discerned. 



The angular and columnar layers can not be considered layers of the 

 periderm of the graptolites, though they may correspond to some part of 



