DICRANOGRAPTUS. 177 



thecse appear to be strongly curved. The apertures frequently show strong intro- 

 version and introtorsion. 



Horizon and Localities. — Glenkiln Shales and Lower Hartfell (Balclatchie Beds). 



8. Scotland. — Cairn Hill ; Wandcl Water; Abington ; Glenkiln Burn ; Sowen 

 Docl; Wanlockhead ; Berrybush Burn ; Little Letterpin, Ayrshire, etc. 



Associates. — Var. spinifer is associated with most of the characteristic Glenkiln 

 forms, such as Vicellog. sextans, Nemag. gracilis, Dicranog. ziczac, Leptog. flaccidus, 

 etc. The best specimens are in the collections of Lapworth and the Geological 

 Surveys of Scotland and England. 



Var. longicaulis, Lapworth, MS. Plate XXIV, figs. 8 a— c. 



1872. DicraiKHji-aptiis ramosus, Lapworth, Cat. West Scott. Foss., pi. iv, fig. 80. 



Another common variety of D. ramosus, which has not hitherto been found in 

 Britain at a lower horizon than the Hartfell Shales, is that designated by Lapworth 

 in his collection as var. longicaulis. 



As its name implies, the biserial portion is considerably longer than that of the 

 typical form. It has usually a length of 2 — 3 cm., and is composed of at least 

 20 thecse on each side. Some specimens, indeed, have been found (zone of 

 D. Glingani) in which the biserial portion is nearly 4 cm. long, and includes 33 

 thecse, but these examples are exceptional. 



The characters of the thecse are similar to those of the typical D. ramosus, and 

 are not spinose. 



Horizon and Localities. — Lower Hartfell Shales (zones of Dicranog. Glingani and 

 Pleurog. linearis). 



8. Scotland. — Dobb's Linn ; Hartfell Spa, etc. 



Associates. — Var. longicaulis occurs in association with Dicranog. Glingani, 

 Gorynoides calicularis, Diplog . foliaceus (ami), etc. 



Good specimens are in the collections of the Geologieal Survey of Scotland, 

 the Natural History Museum, the Sedgwick Museum, and that of Lapworth. 



Dicranograptus ziczac, Lapworth. Plate XXV, figs. 3 a — d. 



1876. Dicranograptus ziczac, Lapworth, Cat. West Scott. Foss., pi. 3, fig. 77. 



1877. Dicranograptus ziczac, Lapworth, Proc. Belfast Nat. Field Club, Grapt. Co. Down, p. 141, pi. 6, 

 fig. 42 a, 



Polypary somewhat variable in form, consisting of a very short biserial portion 

 3 — 4 mm. in length, and two uniserial stipes with characteristic ziczac 



