190 BRITISH (JRAPTOLITES. 



specimens the greater length of the virgella is the most obvious point of 

 difference. 



CI. medius agrees with CI. Tomquisti in the possession of a conspicuously long 

 virgella and in the general characters of the thecse, but in CI. Tomquisti the sicula 

 is longer and less imbedded in the polypary, and the septum is not complete until 

 the level of the eighth thecal pair. 



Horizon and Localities. — Birkhill Shales (zones of Diplog. vesiculosus and 

 Monog. gregarius). 



S. Scotland: Dobb's Linn; Lockerbie; Duffkinnel, near Wamphray, etc. 

 Wales: Llanystwmdwy ; Pennant, Llanbrynmair. Lake District : Skelgill. 



Associates, etc. — CI. medius is most abundant in Britain in the zone of Diplog. 

 vesiculosus ; it is also fairly common in the lower part of zone of Monog. gregarius 

 at the top of the Lower Birkhill Shales, and is met with occasionally at a 

 slightly higher horizon ; it is usually associated with Diplog. vesiculosus, Dimorpliog . 

 Swanstoni, Monog. gregarius, M. tenuis, M. triangulatus, CI. rectangularis, and 

 Diplog. physophora . 



Collections. — Sedgwick Museum, Fearnsides, and the Authors. 



Climacograptus Tomquisti, sp. nov. Plate XXVI, figs. 6 a—f. 



1876. Climacograptus rectangularis, Lapworth, Cat. West Scott. Foss., pi. ii, fig. 50. 



1877. Climacograptus scalaris var. rectangularis, Lapworth, Grap. Co. Down, Proc. Belfast Nat. 

 Field Club, p. 138, pi. vi, fig. 32. 



1897. Climacograptus rectangularis, Tornquist, Diplog. and Heteroprionidae of Scanian Rastrites 

 Beds, Acta Reg. Soc, Physiog. Lund, vol. viii, p. 8, pi. i, figs. 16 — 21. 



Polypary 1 — 4 cm. in length, widening within 1*5 cm. to a maximum breadth 



of 2 mm., which is maintained to the distal extremity ; sicula 2 mm. in length, 



only partially concealed ; virgella robust and long, generally attaining a 



length of 10 mm. or more. Septum, partial until level of eighth thecal 



pair. Thecas twelve to ten in 10 mm. of the form of those of CI. scalaris. 



Description. — The sicula is long, and is free for nearly the whole of its apparent 



length on one side, giving to the proximal end an appearance closely resembling 



that of a Dimorphograptus. 



The proximal end is somewhat abnormal for a Climacograptus', th. I 2 is so 

 unusually long that its aperture is above the level of that of th. 2 1 , while its 

 direction of growth is so peculiarly upward, instead of outward and upward, that 

 the sicula is left entirely free on one side; nevertheless the thecce appear to develop 

 in their usual order. 



The virgula is not often preserved as a distal prolongation, but occasionally 

 projects 1.0 — 15 mm. beyond the polypary; it is very slender as a rule, a fact 

 w h it-li no doubt accounts for the comparative rarity of its preservation. 



