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 surcularis. Hall. PI. 7, fig. 12. Locality — Bally- 
grot. 
87. Sp. 3. Ccenograptus pertenuis. Lapw. PI. 7, fig. 13. (Catl. Western 
Scottish Fossils, 1876. PI. 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. Hydrothecae 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. PI. 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. Rastrites 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. 1. Dictyonema Moffatensi^. Lapw. PI. 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 ; 
