PLATE IV. 



P HTLLOQRAPTUS ILICIFOLIVS, HaLL. 



Fig. 1. An enlarged figure of a compressed specimen, showing the faces of two adjacent folia; 

 the margins being broken away so as to show the cell-openings. 



" 2. A specimen of the natural size, where one folium is broken away, not quite so far as the 

 axis, leaving the bases of the cellules visible. 



" 3. A specimen compressed in the same manner as figs. 1 and 4; the upper foUa have, how- 

 ever, been separated, except the bases of a few of the cellules above the middle of 

 the figure, leaving the other two folia imbedded in the shale, and showing the bases 

 of their cellules ascending from the axis (enlarged to three diameters). 



" 4. An enlargement of a specimen which is imbedded obliquely, as in fig. 1, or in a direction 

 as if tbe theoretical figure 5 were vertically compressed, leaving no visible axis. In 

 the lower half of the specimen the fossil has been separated in the opposite slaty 

 .aminas, leaving only the impression of that side, which also shows no axis. In the 

 upper half of the specimen the cellules are filled and well preserved, and on the left- 

 hand side the apertures are conspicuous (enlarged to three diameters). 

 A restoration of the form of P. ilicifolius, showing the four divisions, which are repre 

 sented as cut through transversely, exhibiting the cell-cavities. 



Phyllograptus anna. Hall. 



Pig. 6. A specimen with the folia obliquely compressed. 

 " 7. An enlargement of a specimen where the two lateral folia remain, showing the cells of the 

 division which has been broken off in the separated laminae of the slate. The 

 surface is distinctly striated. 



Retiograptvs tentaculatus, Hall. 

 Fig. 8. An individual of the natural size, with the marginal reticulations nearly entire. 



R.ETIOGRAPTUS EUCSARIS, HaLL. 

 Fig. 9. An illustration of the compound form of the genus, enlarged to four diameters. 



Dendrograptus frvticosus. Hall. 

 Fig. 10. A frond which is apparently nearly entire. 



Dendrograptus gracilis, Hall. 



Fig. 11. An enlargement from one of the branchlets, showing the striate surface and the deep 

 indentation of the cellules. 



Dendrograptus f {Gallograptos ?) diffusus, Hall. 



Fig. 12. An enlargement, showing the cell-apertures. All the specimens observed of this species, 

 are extremely compressed. 



Gallograptvs salteri, Hall. 



Fig. 13. Fragment of frond, showing the non-celluliferous side. 

 " 14. An enlargement from the non-cclluliferous side, showing a few transverse dissepiments at 

 irregular intervals (figure enlarged). 



