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 Dicettograptus elegans, Carr. Sp. Locality — Ballygrot. 



Genus XIII. Didymograptus. M'Coy; (Pal. Foss., p. 9.) 



83. Sp. 1. Didymograptus superstes. Lapw. PI. 7, figs. 15 a-b. (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. Hydrothecse 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 sagittaruts. (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 serralulus (Hall). 



Localities— Ballygrot and Craigavad. 



Genus XIV. Leptograptus. Lapworth. (Geol. Mag. 1873, p. 558.) 



84. Sp. 1. Leptograptus flaccidus. Hall. PI. 7, fig. 14. Localities — Car- 



nalea, Orlock Point, and Ballygrot. 



Genus XV. Cgenograptus. 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. Casnograptus gracilis. Hall. PI. 7, fig. H- Localities — Bally- 



grot and Craigavad. 

 None of the Scottish examples of this species give evidence of having been 



