Lapworth— Graptolites of Co. Down. 143 



composed of four branches, as indicated in the American specimen figured by 

 Hall. (Grapt. Quebec Group, p. 14.) 



86. Sp. 2. Ccenograptus surculatis. Hall. PL 7, fig. 12. Locality— Bally- 



grot. 



87. Sp. 3. Ccenograptus pertenuis. Lapw. PL 7, fig. 13- (Catl. Western 



Scottish Fossils, 1876. PL 3, figs. 66, 67.) 

 Polypary consisting of two simple or compound monoprionidian flexuous 

 and extremely slender branches, proceeding in opposite directions from 

 the central portion of a well-marked sicula. Hydrothecse 16 to the 

 inch, of the type of those of Ccenograptus gracilis, 

 The forms C. explanatus, and C. nitidulus figured by myself in the Catl. 

 Western Scott. Fossils may be distinct species, or merely varieties of the pre- 

 sent form. It will consequently be better to defer their description till this 

 point has been satisfactorily determined. Locality— Ballygrot. 



Genus XVI. Thamnograptus. Hall. 



88. Sp. 1. Thamnograptus typus ? Hall. PL 7, fig. 16. 



This form has only been procured in small fragments in the dark shales of 

 County Down. It occurs locally in great profusion in the Glenkiln Beds of 

 the South of Scotland. Some comparatively perfect and well preserved 

 examples from these beds lately added to my collection, make it clear that 

 different portions of the polypary are so distinct in their characters, that they 

 have been considered as belonging to distinct species. Rasttites Barrandei of 

 Hall is a true Thamnograptus, and ought probably to be referred to the present 

 form. Localities — Ballygrot and Craigavad. 



Genus XVII. Dictyonema. Hall. (Palaeontology of New York, Vol. ii., 

 p. 174.) 



89. Sp. I. Dictyonema Moffatensi^. Lapw. PL 7, fig. 17. 



Polypary about an inch in length and one-third of an inch in maximum 

 diameter, cupshaped, of an elongate semi-elliptical form; composed of 

 slender, radiating, free, comparatively straight branches, with slightly 

 crenulated margins ; transverse dissepiments distant, scarcely visible ; 



