Lapworth— Graptolites of the Co. Down. 133 



40. Sp. 8. Diplograptus Hughesi. Nich. PI. 6, fig. 14. Locality— Coalpit 



Bay. 



41. Sp. 9. Diplograptus itistctiformis. Nich. PI. 6, fig. 15. Locality — 



Ballygrot. 



42. Sp. 10. Diplograptus folium. His. PI. 6, fig. 16. Locality — Coalpit 



Bay. 



43. Sp. II. Diplograptus truncatus. Lapw. PI. 6, fig. 17, 



Diplograptus pristis, var. truncatus. Lapw. (Catl. Western 

 Scott, Fossils. Plate 1, fig. 28.) 



Polypary diprionidian, sub-fusiform or with parallel margins, one to three 

 inches in length and one-eighth of an inch in maximum diameter; fur- 

 nished proximally with a minute radicle and lateral spines. Virgula 

 invisible. Hydrothecse inclined at an angle of about 45 degrees, 

 linear-tubular, expanding towards the oblique apertural margin and 

 ornamented with minute transverse striae. 



There are several varieties of this species in the South Scottish rocks, but 

 they agree generally in the foregoing characteristics. Some smaller and wider 

 examples of this form are almost inseparable from Dip. palmeus. Forms pre- 

 served in relief show no trace of a longitudinal septum on one of the lateral 

 faces. I formerly referred this species to Diplograptus pristis of Hisinger, but 

 Swedish specimens of the latter show a polypary and hydrothecee of the general 

 type of Diplograptus quadrimucronatus (Hall). 



44. Sp. 12. Diplograptus foliacms. Murch. PI. 6, fig. 18. Locality — 



Ballygrot. 



45. Sp 13. Diplograptus vesiculosus. Nich. PI. 6, fig. 19. Locality — 



Coalpit Bay. 



46. Sp. 14. Diplograptus quadrimucronatus. Hall. PI. 6, fig. 20. 



In the Scottish examples referred to this species, four rigid spurs are usually 

 given off, one from each of the angles of the prismoid polypary at a normally 

 uniform height corresponding to the position of the sixth or seventh hydrotheca, 

 counting from the initial extremity. 



In the Irish forms collected by Mr. Swanston the spurs are sometimes 



