Lapworth— Graptolites of Co. Down. 131 



25. Sp. 18. Monograptus gregarius. Lapw. PI. 5> &?■ 4- Locality — The 



characteristic fossil of the central portion of the Birkhill shales. It 

 occurs in myriads in the black shales of Coalpit Bay. 



26. Sp. 19. Monograptus argutus. Lapw. PI. 5, fig. 5. 



The accompanying figure, as well as that illustrative of the original 

 description ot this species, was taken from a cast of a compressed example. In 

 specimens preserved with their relief the hydrothecae resemble those in 

 Dicellograptus, having a deep excavation in the distal portion of their outer 

 wall, while the aperture opens obliquely outwards, partly overlapping the 

 lateral wall of the common canal. Locality — Coalpit Bay. 



27. Sp. 20. Monograptus Sandersoni. Lapw. PI. 5, fig. 8. Localities — 



Coalpit Bay and Tullygarvan. 



28. Sp. 21. Monograptus tenuis. Portlock. PI. 5, fig. 10, Localities — 



Coalpit Bay and Tullygarvan (?) 



29. Sp. 22. Monograptus atttnuatus. Hopk. PI. 5, fig. 3. Locality — 



Coalpit Bay. 



Genus III. Dimorphograptus, provisional genus. Lapworth. (Geo. Mag., 

 1876, p. 545.) 

 Examples of this genus are found in great profusion both in Ireland and 

 Scotland, and in all we find the characteristic mono-diprionidian polypary. 

 Nevertheless, in the complete absence of specimens preserved in relief, I have 

 grave doubts of the validity of the genus. We meet with occasional examples 

 in which we have a hint of a second series of hydrothecae in the proximal por- 

 tion. It is just possible that in this group the concavo-convexity of the poly- 

 pary general among the diprionidian Graptolites is carried to excess ; and that 

 the partial invisibility of the second series of hydrothecse is due to their lying 

 almost parallel with those of the first series. 



30. Sp. 1. Dimorphograptus Swanstoni. Lapw. PI. 6, fig. 5. 



A most remarkable and very distinct little species. It occurs in admirable 

 preservation in the Coalpit Bay division of the County Down black shales, but 

 has not hitherto been detected in the corresponding zone of the Moffat Series. 

 Geinitz figures an example of this species from the Kicsel-scheifer of Central 

 Germany. (Die Versteinerungen, Taf. 1, fig. 25.) Locality — Coalpit Bay. 



K 



