156 Mr. C. Lapworth on new British Graptolites. 



pressed specimens originates a long oblique and acuminate 

 denticle, occasionally prolonged into a short spine. 



Compressed examples of this form admit of immediate 

 identification, as the distal portions of the theca form a series 

 of broad acutely triangular denticles running down the ven- 

 tral edge of the polypary, directed towards its proximal extre- 

 mity and projecting outwards to a distance equal to at least 

 one third of the diameter of the polypary itself. 



Specimens from different localities vary greatly in the 

 number of hydrothecas upon the same longitudinal extent. 

 The thecal walls are of the form of those of Monograptus 

 priodon, Bronn. In young examples the polypary is short 

 and stout, augmenting its original diameter with great rapidity, 

 with closely approximated hydrothecas. 



This form may be distinguished at a glance from M. riccar- 

 tonensis. It is more intimately allied to M. crassus, from 

 which it differs principally in the form of the thecal walls, 

 the greater eversion and denticulation of the apertural margin, 

 and in the more closely set and overlapping hydrothecEe. 



Horizon and Locality. Rare in the Riccarton beds of Rox- 

 burgh and Kirkcudbright, and in the Wenlock shales of 

 Siluria ; common in the Coniston Flags of Westmoreland. 



10. Monograptus M'Coyi, Lapw. 



Monoqraptus M'Coyi, Lapworth, Graptolites of County Down, Trans. 

 Belfast Nat. Field-Club, 1876-7, pi. vi. fig. 2, p. 130. 



A diagnosis and figure of this form are given by M'Coy, in 

 his l Palaeozoic Rocks and Fossils,' under the title of Graptolites 

 latus*. It is not unlikely that it may eventually be shown 

 to be the species upon which Murchison founded his Grapto- 

 lites ludensis, in which case the more recent title must be 

 suppressed. In the adult form of the polypary the hydrothecaj 

 are from four to five times as long as wide, and the denticle 

 is short and destitute of ornamentation. 



Horizon and Locality. Examples, apparently of this species, 

 from the Lower Ludlow rocks of Siluria are preserved in the 

 Ludlow Museum. M'Coy's original example was procured 

 from the Wenlock (?) of Builth Bridge. 



11. Monograptus Hisingeri, Carr., var. nudus, var. nov. 

 (PL IV. fig. 7a, I, c.) 



Monograptus Hisingeri, Lapworth, Geological Magazine, 1876, pi. xii. 

 figs. 1 a-\ c, &c. 



This form has been already so minutely described (loc. cit. 

 * M'Coy, Palaeozoic Rocks and Fossils, pi. 1 B. fig. 7. 



