DIPLOGRAPTUS. 247 



somewhat abundantly in the Lower Girvan Rocks of the Girvan District, where it 

 is often found in a beautiful state of low relief. It is commonly associated with 

 Cryptog. t ricomis, Gl. bicornis, CI. Scharenbergi, Dicranog. tardiusculus, and other 

 forms. 



Collections. — Geological Survey of Scotland, Mrs. Gray, and Lapworth. 



Sub-genus Glyptograptus, Lapworth. 



In the forms included in the sub-genus Glyptograptus there is not so much 

 variation as in some of the other sub-genera ; the polypary seems to have been 

 typically more or less circular in section, while the thecse only show a marked 

 departure from the shape of those of the typical species, Glyptog. tamariscus, when 

 they exhibit a certain degree of torsion in their apertural region (G. sinuatus). 

 The small amount of overlap is highly characteristic of all the members of this 

 sub-genus. 



Group I. 



Glyptograpti, in which the axis of the theca was straight, the thecae semi- 

 circular in section, and the apertural margins undulate; excavations wide and deep. 



Diplograptus (Glyptograptus) tamariscus, Nicholson. Plate XXX, figs. 8 a— d. 



18G8. Diplograpsus tamariscus, Nicholson, Quart. Journ. Clcol. Soc, vol. xxiv, p. 526, pi. ix, 

 figs. 10-13. 



1876. Diplograptus tamariscus, Lapworth, Cat. West. Scott. Foss., pi. ii, fig. 34. 



1877. Diplograptus tamariscus, Lapworth, Grapt. Co. Down, pi. vi, fig. 12. 



1897. Diplograptus tamariscus, Tornquist, Diplograptidae and Heteroprionida? of Scanian Eastrites 

 Beds, Kongl. Fysiog. Siillsk i Lund Forhandl., vol. viii, p. 15, pi. ii, figs. 15 — 19. 



Polypary long and narrow, varying from 7 mm. to 45 cm. in length, and rarely 



exceeding 1 mm. in breadth ; sicula small, septum incomplete. Theca? 



fourteen to twelve in 10 mm., with pronounced sigmoid curvature, 



alternate; overlap slight, free edge rounded, apertural margin even or very 



slightly undulate, horizontal or slightly introverted in profile view. 



Description. — The polypary varies considerably in size from 7 mm. to 4 - 5 cm. ; 



it widens gradually from an initial breadth of *4 mm. to its maximum breadth of 



about 1 mrn., or rather less when preserved in relief. The sicula has a length of 



1 mm., the virgella when preserved may measure 5 mm. Th. I 1 originates close 



to the aperture and grows down below it for a short distance before turning upward 



