STUDY OF THE GRAPTOLITES. 231 



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

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

 species 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. anten- 

 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. 3Iode of Meprodtiction and Development in the GrajitoUtidw. 



As already remarked, the Graptolites proper are now generally referred 

 by authors to the Radiata — Htjdrozoa; 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 Graptolitidae, since the Graptolites proper disappear 

 from existence in the Silurian period ; and the latest form of Grap- 

 tolitidae {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 develop- 

 ment are not so 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 

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

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

 enlarged, form elongated sacs with swollen extremities, which become 

 finally dehiscent; and then, as I suppose, discharging the ovules or 

 germs, are gradually absorbed or dissipated. 



Although these sacs are distinctly defined, they have scarcely any 

 apparent substance, except along the lateral margins, which are limited 

 by a filiform extension resembling the solid axis of a Graptolite. There 



