540 NEW YORK STATE MUSEUM 



periderm had originally consisted of the same chitinous substance as that 

 of the sertularians. 



In 1893 Sollas published some notes on the peridermal layers of Mono- 

 graptus, giving their dimensions. 



Perner used specimens of Monograptus and Retiolites embedded in lime- 

 stone to prepare his sections. By means of these he was enabled to discern 

 four different layers, namely (1) the epidermis (coiiche epidermique), which 

 appears as a fine, brown line, (2) the black layer (con<-he noire), a thick, black, 

 supposedly chitinous band, (3) the angular layer (coucJie a coins), the thickest 

 layer, which is brown and marked by angular or zigzag lines, (4) the 

 columnar layer {pcniche a colonnettes), a thin, brown layer, consisting of small 

 columns and possessing a darker layer, suggesting an internal epidermis. 



Wiman [1895, p.39] was unable to discern anything more than the black 

 layers in sections of Monograptus, made from Swedish material, but he 

 observed the external epidermis and the black layer in sections of Dendro- 

 graptus and the external and internal epidermis and the black layer in 

 sections of Monograptxis priodon from Perner's locality. In decol- 

 orized specimens of Diplograptus he was also able to discern the black 

 layer with its growth lines and the superjacent epidermis in continuous 

 patches. 



Giirich [1896] has revised Perner's observations on the periderm of 

 Monograptus and found that the angular layer {couche a coins) consists of 

 calcite crystals and is secondarily formed during fossilization ; and that the 

 brown layers observable outside and inside of the black layer are zones of 

 pigment which either are derived from the black layer or formed a superficial 

 layer of the same. The epidermis and columnar layers have not been 

 observed by Giirich. 



A layer of graptolite bed 2 (Tetragraptus zone) at the Deep kill, in 

 which the graptolites are retained uncompressed in pyrite, provided the 

 present writer with material for thin sections, principally specimens of 

 Phyllograptus ilicifolius and branching dichograptids. In these 

 the walls consist uniformly of three layers, viz the black layer, the angular 



