142 
Lapworth— Graptolites of Co. Down. 
at a small angle, and are so curved that they cross and recross each 
other distally in the figure of 8. Axillary spine prominent, lateral 
spines undeveloped. Hydrothecae 24 to 28 to the inch, of the form 
of those of Dicellograptus elegans , Carr. Sp. Locality — Ballygrot. 
Genus XIII. Didymograptus. M‘Coy; (Pal. Foss., p. 9.) 
83. Sp. 1. Didymograptus super stes. Lapw. PI. 7 > fig s * *5 a '^- (Catl. 
Western Scottish Fossils. PI. 3, fig. 74 *) 
Polypary consisting of two simple monoprionidian branches, of great length, 
attaining a maximum diameter of one-tenth of an inch, within the first 
three inches of their extent ; broadly curved and including a ventral 
angle of about 120 degrees. Hydrothecae 24 to the inch, inclined at 
an angle of 40 degrees, rapidly expanding in the direction of the aper- 
tural margin, which is deeply concave, and forms a broad triangular 
denticle. 
Perfect specimens of this well-marked species are rarely detected ; but the 
broad and slightly curved branches are numerous both in Scotland and Ireland 
in the typical Glenkiln Shales. This is in all probability the same species as 
that figured by Hall as Graptolethus Sagittarius . (Pal. New York. Vol. I., 
Plate 74, fig. 1.) It is also associated here, as in North America, with a 
slender species which appears to be the same as Didymograptus serratulus (Hall). 
Localities— Ballygrot and Craigavad. 
Genus XIV. Leptograptus'. Lapworth. (Geol. Mag. 1873, p. 558.) 
84. Sp. 1. Leptograptus fiaccidus. Hall. PI. 7 > fig* I 4 * Localities — Car- 
nalea, Orlock Point, and Ballygrot. 
Genus XV. Ccenograptus. Hall. (Modified.) (Hall, Annual Report, 
1867, p. 179.) 
So far as at present known this genus differs from Pleurograptus (Nich.), 
in the possession of an initial cross-bar, formed by the persistent sicula. 
85. Sp. I. Ccenograptus gi'acilis. Hall. PI. 7 > fig- II# Localities Bally- 
grot and Craigavad. 
None of the Scottish examples of this species give evidence of having been 
