166 BRITISH GRAPTOLITES. 



apertures opening within a shallow and approximately semicircular excava- 

 tion, which occupies about one third the width of the stipe. 

 Description. — The biserial portion of the polypary is short, commonly com- 

 posed of from 4 to 6 thecaa on each side, and is of fairly uniform width throughout. 

 The uniserial stipes are also short (2 cm. or more) and are typically straight, with 

 a uniform width of rather less than 1 mm. They diverge at an angle of about 

 40°, and the angular form of the axil is characteristic of the species. 



The structure of the proximal end is somewhat obscure in the specimens at our 



disposal, but the mode of development of the earliest thecse is undoubtedly similar 



to that in all other Dicranograpti. The sicula, being 



Fig. 103. — Dicranograptus Clin- • •■,■, i 



gani, Carr. visible only m one aspect (obverse) or the polypary, 



is rarely seen. It appears to be narrow and about 1 

 mm. in length. Thecse l 1 and thecse l 2 are far smaller 

 than any of those subsequently developed, measuring '8 

 mm. in length. 



The remaining thecse of the biserial portion and 

 those of the uniserial stipes measure 1*5 to 2 mm. ; they 

 generally overlap for half their length. 



Affinities. — D. Clingani resembles in general form I). 



Enlargement of PI. XXIV, fi"\ 1 q, , i 7~> 7 • t 1 l j> i j_i ;i v 



showing type of thecal rectus and V. brevieaulis ; but from both or these it may 



be distinguished by the relative shortness of the 

 biserial and uniserial portions and by the characters of the thecse. From all other 

 Dicranograpti its form affords a sufficiently distinguishing character. 



Horizon and Localities. — Hartfell Shales. 



8. Wales : Robeston Wathen. N. Wales : Railway Cutting, Conway. 

 8. Scotland : Dobb's Linn ; Hartfell ; Berrybush Burn, etc. Ireland : Carnalea, 

 Coalpit Bay. 



Associates, etc. — I). Clingani is a fairly common fossil in the Hartfell Shales 

 (zone of D. Clingani) of South Scotland, and also occurs in some abundance at 

 Conway. In S. Scotland it is usually associated with Bicellog. Morrisi, Dicellog. 

 Forchammeri, Climacog. bicomis, Diplog.foliaceus (anct), Dvplog. truncatus, Corynoides 

 calicularis, and other forms. The best specimens known to us are in the 

 collections of Lap worth, the Geological Survey of Scotland, the Sedgwick Museum, 

 and the British Museum of Natural History. 



Group II. — Type Dicvanog. tardiusculus. 



Bicranograpti in which the thecse have gently curved ventral walls and horizontal 

 apertures. 



