198 TWENTIETH REPORT ON THE STATE CABINET. 



growth the cell-walls are continued, gradually contracting above, and, after 

 becoming free from the adjacent cellule, form a slender gradually curving 

 tube, which in mature individuals has its orifice directed backward. 



In Dendrograptus^ the form of the orifice and outline of the aperture 

 present variations similar to those of the simple uniserrate graptolites ; 

 but some species show modifications in the form of the cellule which do 

 not accord with the more simple forms. In Dictyone?na, the cellules are 

 not fully known ; the orifices are marked by a prominent mucronate exten- 

 sion, and apparently simulate the more common forms of graptolites (fig. 5, 

 Plate i). 



In the bi-celluliferous species the compressed specimens present the 

 plane of the orifice, sometimes rectangular to the general axis, sometimes 

 with the outer margin a little advanced, making an acute angle with the 

 axis of the cellule; while sometimes the plane of the margin of the aperture 

 is rectangular to the axis of the cellule, or rarely makes with it an obtuse 

 angle. The cellules of Retiograpiics, which have not yet afforded means 

 of satisfactory examination, apparently have their orifices nearly rectan- 

 gular to the general axis of the stipe. 



In one of the forms of the bi-celluliferous graptolites, the cellules are 

 sub-elliptical tubes, with an orifice of corresponding form, without extension 

 -beyond a slight thickening or callosity at the margin of the orifice. The 

 plane of the cell-aperture in this one makes an obtuse angle with the 

 direction of the general axis. 



In forms like G. bicornis, the external orifice is transversely oval, with 

 or without a projection and thickening of the test from the cell-partition 

 above the orifice, or extension of the test. 



4. Ornaments of the Test. — The compressed condition in which the 

 graptolites usually occur, is unfavorable to the preservation of any minute 

 surface-markings, or ornaments of the test. 



In many of the species, fine striae, parallel to the margins of the cell- 

 epertures, are perceptible, and in the larger number of species this mark- 

 ing is all that is preserved. There is sometimes a granular appearance 

 of the surface ; but I have not been able to satisfy myself that this is the 

 actual surface-texture, and it may be a condition induced by mineralization. 

 In a few examples there is a row of minute pustules at the base of, and 

 corresponding to the cellules. 



The stems and branches of Dendrograptiis, Callograptus, and Dictyo- 

 nema are irregularly striated. In typical species of RetioUtes the test is 

 finely reticulate ; while in the species from the Quebec group, this texture, 

 if existing, is so fine as not to be readily resolved by an ordinary lens. 

 The surface, however, has not the appearance of entire smoothness, as in 

 most of the ordinary graptolites. 



The chief ornaments of these bodies are the mucronate extensions of 

 the test, usually from the lower margins of the cellules, but sometimes 

 from the upper margins. In ordinary forms of the species, with single, 



