STUDY OP THE ORAPTOLITES. 243 



stipes, regarding as true branches only the subdivisions which take place 

 after the commencement of the cellules. 



The Genus Nereograptus* of Geinitz, proposed by that author to 

 include such forms as Nereites, Myrianites, and Nbmertites of Murohi- 

 SON, and Nemapodia of Emmons, etc., can scarcely be admitted into the 

 family of Graptolitidaj, since all the American species referred to the 

 first three named genera have no texture or structure like graptolites, 

 and (as I have elsewhere shown) appear to be referable to the tracks or 

 trails of some marine worms or other animals upon the sea-bottom ; 

 while Nemapodia is simply the trail of an existing slug or worm upon the 

 slightly lichen-covered surfaces of the slates. t 



The Genus Glossograptus of Emmons is founded upon a species of 

 DiPLOGRAPTUS with ciliate appendages on the cell-margins ; and no char- 

 acters are given to show its generic distinction. The typical species of 

 Nemagraptds (iV. elegans) is apparently a part of an individual of Grap- 

 tolithus gracilis, or of some similar form ; while the relations of the second 

 species of the genus (iV. capillaris), an elongate, flexuous, filiform body 

 with a few branches at irregular intervals, can scarcely be determined 

 from the figure given. 



The typical and only species of StaurograptusJ of the same author is 

 a very remarkable form of extremely minute proportions. Its mode of 

 growth and subdivision of stipes, if accurately represented in the figure, 

 are unlike anything known among this family of fossils, and it merits 

 generic distinction. 



The term Diplograptus is properly applied to such forms as GruptoU- 

 thus pristis, of Hisinger, G. palmefiis, of Barrande (excepting figs. 5 and 

 6) ; G. foliacms, of Murchison, and G. amplexicaulis of this memoir ; where 

 the cellules are disposed in parallel ranges on the two sides of the central 

 axis, and are of the same or similar form and arrangement with those of 

 the monoprionidian form G. Sagittarius^ and with others of that type; 

 the reason for the proposed separation being in the double range of 

 cellules only. 



In the ordinary forms of Diplograptus (Plate iii, figs. 1-7), as in the 

 ordinary monoprionidian types, the cellules are usually closely arranged, 

 and overlapping each other for a part of their length. In a single 



* Nereograpsus : Die Verstein. Grauwacken formation, etc., Graptolithen, p. 27. 



t These markings can be easily removed from the surface of the laminas by washing with water ; ' 

 and they can be traced over the exposed surface of the edges of the successive lamin*. 



I Glossograpsds, Staurogeapsus, Nemagrapsus (Emmons) : American Geology, Part ii, 

 pages 108 and 109. 



