STUDY OF THE GRAPTOLITES. 211' 



simply the trail of an existing slug upon the slightly lichen-covered sur" 



faces of the slates.* 



The Genus Glossograptus of Emmons is founded upon a species of 



Diplograptus with ciliate appendages on the cell-margins ; and no charac- 

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

 Nemagraptus {N. elcgans) is apparently a part of an individual of 

 Graptolitlius gracilis, or of some similar form ; while the relations of the 

 second species of the genus [N. 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 Staurograptusi 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 Graptoli- 

 tkus prisiis, Hisinger; G. palmeus, Barrande (excepting figs. 5 and 6); 

 G. foliaceus^ Murchison, and G. amplexicaulis oi 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 

 monopriouidian form G. Sagittarius, and with others of that t3'pe ; 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 monopriouidian types, the cellules are usually closely arranged, 

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

 {G. putillus, from the Hudson-river formation in Iowa), which has come 

 under my observation in some well-preserved fragments, we have so far a 

 modification of the general arrangement of the cellules that the apex of 

 one barely reaches the base of the next succeeding. The stipe is a strong, 

 elliptical tube with a flattened central solid axis, the line of which is 

 marked on the exterior by a longitudinal undulating groove (fig. 10, PI. ii). 

 The surface is strongly striated transversely, and the sides studded with 

 tubular cellules, which are alternatfdy arranged. These cellules are sub- 

 oval, flattened on the side adjoining the body of the graptolite, curving on 

 the exterior free portion, and obliquely flattened at the base just above the 

 aperture of the cellule next below, as shown in the profile view (fig. 11, 

 Plate ii). The exterior test of the common body is swollen in oblique 

 undulations in the direction of the base of the cellules, or where the indi- 

 vidual buds take their origin ; and the axis is curved towards the opposite 

 side, as shown in fig. 10. 



The transverse diameter of the stipe is about two-thirds as great as the 

 longer diameter. The celluliferous face of the stipe shows broad elliptical. 



* These markings can be easily removed from the surface of the laminae by washing with 

 water; and they can be traced over the exposed surface of the edges of the successive 

 lamina). 



t Glossograpsus, Staurograpsus, Nemagrapsus: E.mmoms, American Geology, Part ii, 

 pages 108 and lO'J. 



