Nicholson — On Graptolites. Ill 



tical with the GraptoIitTius flaccidus of Hall, which occurs in the 

 Utica Slate, the American equivalent of our Upper Llandeilo Eocks. 



1 am not aware that it has been before recognized as occurring in 

 G-reat Britain, but I have found it in tolerable plenty in the anthra- 

 citic shales of Dobbs' Lhin and Hart Fell, near Moffat. For its 

 specific characters I may refer to Hall's description, (Graptolites of 

 the Quebec Group, Supp. p. 143, Plate II., Figs. 17-19.) 



D. flaccidus is at once distinguished from all other species of 

 Didymograpsus, by the slender and flexuous stipes (Fig. 1), each of 

 which may attain a length of nearly half a foot, without showing 

 any sign of a termination. The cellules are on the convex side of 

 the frond, the denticles angular or rounded. The mucro is on the 

 concave side of the frond, sometimes short and obtuse, as in Hall's 

 specimens ; sometimes, however, attaining a length of one-tenth of 

 an inch. In most of the specimens in my possession, the margin 

 opposite to the mucro is ornamented with three small spines (Figs. 



2 and 3), one directly opposite to the radicle, and one springing 

 from the apes of the first cellule on each side. On a cursory examin- 

 ation the entire frond may be confounded with Graptolithus tenuis, 

 unless the presence of a radicle should be detected. 



Diplograpsus quadri-mucronatus. Hall, sp. (Plate YII. Figs. 6-8.) 

 This is another Utica Slate species, which I have found in the shales 

 of Dobbs' Linn, though it is not of common occurrence. It has a 

 considerable resemblance to D. WMtfieldi, Hall (Fig. 4), but is 

 altogether a larger form, and is distinguished by the fact that each 

 cellule is provided with two mucronate points, one arising from each 

 angle, whereas, in the latter species, there is only one such mucro to 

 each denticle. For the specific characters of I), quadri-mucronatus. 

 Hall's description should be consulted. (" Graptolites of the Quebec 

 Group," Supp. p. Ill, plate xiii. figs. 1-10.) 



Diplograpsus WMtfieldi, Hall, sp. (Plate YII. Figs. 4 and 4a.) 

 I believe this species has usually been confounded with D. mucro- 

 wafiis. Hall, (Fig. 5), especially as they often occur together. The 

 two are, however, distinguished from one another by good charac- 

 ters. In D. WMtfieldi the denticles are " shallow and angular," 

 whilst the mucros are rigid, and maintain a persistent horizontal or 

 slightly upward direction. In I). Mucronatus, on the other hand, 

 the denticles are prolonged into slender and prominent teeth, 

 fm-nished at their extremities with flexible spines, which have no 

 constant position, but are twisted in every direction, (see Fig. 5a.) 

 For the description of B. WMtfieldi, see Hall's Palseontology of New 

 York, Yol. iii. supp. p. 516. Loc. — Common in the anthracitic 

 shales of Glenkiln Burn, Dumfriesshire. 



Germs of Graptolites (Plate YII. Figs. 21-24. The occurrence 

 of minute bodies, possessing a graptolitic texture, provided with 

 a corneous envelope, and differing in form from all known spe- 

 cies of graptolites, was first investigated by Professor James Hall, 

 to whom we owe so much of our knowledge of the Graptolitidce. 

 (See Palaeontology of New York, vol. iii., supplement and " Grap- 

 tolites of the Quebec group," pp. 33-35 ; plate B., figs. 12-19). 



