CRYPTOGRAPTUS. 295 



the typical forms of the sub-group in the marked protraction of the proximal part 

 of the polypary. 



The general characters of the thecse with their acuminate margins should be 

 sufficient to distinguish G. acuminatus from the other species here grouped as 

 Gephalograpti. 



Horizon and Localities. — Lower Birkhill Shales (zone of G. (?) acuminatus). 



8. Scotland : Dobb's Linn ; Duffkinell Burn ; Garple Linn ; etc. Lake 

 District : Browgill. 



Associates. — Ceplialog. (?) acuminatus is a common fossil in the lowest beds of 

 the Birkhill Shales wherever they are developed ; it is commonly associated with 

 Climacog. normalis. 



Collections. — Sedgwick Museum, Marr, Lapworth, and the Authors. 



Genus CRYPTOGRAPTUS, Lapworth. 

 1880. Cryjitograjdiis, Lapworth, Ann. Mag. Nat. Hist. [5], vol. iv, p. 174. 



Polypary concavo-convex, bilaterally symmetrical, biserial, and of uniform 

 breadth throughout. Test delicate and (?) punctate. 



Thecse rhomboidal, short, inclined at a high angle, with sharp sigmoid curvature 

 in apertural region only ; apertural margins strongly everted, but lying 

 within the general ventral margin. 



One of the most characteristic features of the Gryptograptus polypary is its 

 uniformity in breadth throughout its length, but, as a result of its concavo-convex 

 section, the appearance when compressed is very different in the obverse and 

 reverse aspects. In the obverse aspect the thecal apertures can be made out as a 

 general rule, and the polypary appears somewhat narrower than when viewed 

 from the reverse aspect, when the only trace of the presence of thecse that can be 

 detected is the crenulation of the ventral margin. 



The theca3 are peculiar ; they are inclined to the general direction of the 

 polypary at a high angle for the greater part of their length, but exhibit sharp 

 sigmoid curvature in the immediate region of the aperture, so that for a very 

 short distance the thecal axis lies parallel to the axis of the polypary in a similar 

 manner to that characteristic of the thecse of the majority of Glimacograpti. The 

 free edge of each, however, is exceptionally short, and the apertural margin 

 instead of being horizontal is strongly everted. From the lower end of the free 

 edge of the thecse a spine may be given off. The free edge is so short that in 

 greatly compressed specimens it shows merely as a rounded knob or denticulation 

 (G. tricornis), or, where the thecse are spinose, it is drawn out and apparently 

 merged with the spine itself (G. Hophinsoni). 



