200 TWENTIETH REPORT ON THE STATE CABINET. 



These ornaments are not always uniformly developed in the same species, 

 or even in the same individual. In the larger proportion of specimens of 

 G. ramosus, the margins of the cellules are apparently plain ; but in the 

 cellules of the simple part of the stipe we sometimes find a rigid mucro- 

 nate point, prolonged from the upper margin or limit of the cell-aperture 

 (Plate ii, fig. 20). In G. sextans, the mucronate point is half-way between 

 the two cell-apertures. 



In specimens of G. sextans, and in sonie allied forms from the Hudson 

 River formation at Marsouin, Canada, the stipes and cellules are less 

 fully developed than in those of the same species from Norman's Kill near 

 Albany, while the mucronate extensions from the cell-apertures are more 

 conspicuous. 



Besides these ornaments, there is on each side of the radicle or initial 

 point at the base of most of the diprionidian species of graptolites, a 

 small process, varying in length, and usually directed downwards. These 

 processes are usually short, but often considerably extended ; in some spe- 

 cies they are very slender, while in others they are strong and rigid. In 

 G. pristis they are frequently seen as short slender processes ; while 

 in G. bicornis they are rigid, strong, and slightly curving. In G. aiiten- 

 narius, a congener of the latter, they are slender setiform processes, 

 directed downwards. 



In no species of Phyllograptus have such appendages been observed ; nor 

 have they been seen at the bases of the stipes of Retiolites. 



v. — MODE OF REPRODUCTION AND DEVELOPMENT IN THE GRAPTOLITID^ 



As already remarked, the G-raptolites proper are now generally referred 

 by authors to the Radiata — Hydrozoa ; while some forms, which I include 

 in the family, have been heretofore regarded as reticulate bryozoans, or 

 as gorgonians. 



In nearly all the true bryozoan forms among fossils, we have the means 

 of tracing the relations and analogies, both in manner of growth and 

 reproduction, throughout all the successive geological periods, and in the 

 present fauna. It becomes therefore more difficult to discover such 

 analogies for the Grraptolitidse, since the Graptolites proper disappear from 

 existence in the Silurian period ; and the latest form of G-raptolitidae 

 ( Dictyonema) is not found, so far as now known to me, in American strata, 

 at a later period than the Hamilton formation or Middle Devonian. From 

 this cause the mode of growth and development are not readily understood 

 as in those families which can be traced throughout the geological series, 

 and still find their analogues in the present seas. 



In 1858, I laid before the American Association for the Advancement 

 of Science a notice, with some illustrations of graptolite stipes, bearing 

 what I then regarded, and do still regard, as the reproductive cells 

 {Gonophores). These cells first appear as small ovate buds upon the 

 margins, projecting but little beyond the regular cellules, and, becoming 



