CLIMACOGKAPTUS. 101 



123 a ana b .^u ograptus Affinities. -Unlike the other close allies of 



Tornquisti, sp. nov. Climacog. scalaris, 01. Tornquisti is clearly closely 



K i related to the Dimorphograpti, but since th. I 2 seems to 



develop as usual from th. I 1 and the Dimorphograptid 

 appearance is due merely to its peculiar direction of 

 growth and unusual length, this species must be re- 

 garded as a Climacograptus, of which the charac- 

 teristic features are the following : 



(1) The long sicula, free for nearly the whole of 

 a b its apparent length on one side. 



. , , (2) The long virgella. 



a. Obverse view, showing sicula tree on ' 



the right side. DoWs Linn, Birk- (:3) The incomplete septum until the level of the 



hill Shales. Coll. Biles. . V ' . \ l 



b. Reverse view showing part of sicula eighth thecal pair is reached. 



on left side and long theca I s . En- l . 



largement of part of pi. xxvi, 01. Tornquisti is undoubtedly closely related to 



s ' " ' 01. rectangularis and 0/. medius ; distal fragments of 



CI. Tornquisti and CI. rectangularis are almost indistinguishable, but when the 



proximal end is preserved the longer sicula, long virgella, and less complete septum 



in CI. Tornquisti serve to distinguish it. It is often very difficult to separate it 



from CI. media*, especially in compressed specimens when the details of the 



proximal end are obscure and the septal groove invisible ; but in well-preserved 



specimens the sicula of CI. Tornquisti is seen to be longer and less imbedded in the 



polypary than is the case in CI. medius, and while the septum is not complete until 



the level of the eighth thecal pair, it is always complete in ( 7. medius after the fifth. 



Horizon and Localities. — Lower Birkhill Shales (rare in Upper Birkhill Shales). 



8. Scotland : Dobb's Linn ; Belcraig; Garple Linn. Wales: Big Pit, east side 

 of Pary's Mount; Mona Mine, Pary's Mount; Llanystwmdwy. Lake District: 

 Skelgill. Ireland: Donaghadee, Little River, Pomeroy. 



Associates, etc.- — 01. Tornquisti is a common fossil in the Lower Birkhill Shales, 

 and is especially abundant in the zone of Monog. gregarius. It occurs most 

 frequently associated with Monog. gregarius, Monog. cyphus, Monog. fimbviatus, 

 Monog. triangulatus, CI. rectangularis, CI. innotatus. It is only rarely met with 

 in the higher beds of the Birkhill Shales. 



Collections. — British Museum (Natural History), Sedgwick Museum, Lap worth, 

 Fearnsides, and the Authors. 



Climacograptus minimus (Carruthers). Plate XXVII, figs. 1 a — g. 



1868. Diplograpsus minimus, Carruthers, Geol. Mag., vol. v, p. 125, pi. v, Bgs, 12 a, 121. 



Polypary 1 — 3 cm. in length, increasing gradually in breadth till a maximum 

 of nearly 2 mm. is attained. Sicula visible for 1 nun. of length; virgella 

 fairly short; virgula distally prolonged. Thecse fourteen to cloven in 



