46 BRITISH GRAPTOLITES. 



Be^rription. — The stipes are fairly robust at their origin compared with the 

 averao-e width of the polypary, and measure about '9 mm. ; they widen rather 

 rapidly up to a breadth of 1*2 mm., which is maintained in the greater number of 

 forms ; occasionally, however, in the larger specimens the width may be as much 

 as 1"5 mm., but nevertheless the polypary, as a whole, has a slender appearance. 



The sicula is very long and narrow ; it measures 

 Fia.28.—Did7jmograptvs.ctindc)itiis, 2 b — 3 mm. in leuo'th, and is situated somewhat 



XT 11 O •" 



obliquely with respect to the polypary. The first 

 theca (th. 1') originates at a point slightly above the 

 aperture of the sicula ; the opening appears to be 

 large, but the theca grows away at once with a wide 

 curve, so that the apertural region of the sicula is 



Proximal end impres^on of obverse ^^^[^q f^gg qj^ ^j^g Jgf^ sidc (obvcrSC ^acw). 

 view. Outerside, Keswick. Uoll. ^ ^ ^ 



Woodwardian Museum. The crossinof caual is fairly wide ; it runs 



obliquely from the point of origin of th. 1 ^ to the 

 right apertural edge of the sicula. Tavo phenomena follow from this mode of growth : 



(1) the apparent want of symmetry in the initial part of the polypary, 



(2) the concealment of a large part of the apertural region of the sicula. 



The thecae are slightly in contact in the initial regions of the stipes, but the 

 overlap gradually increases to a maximum of half their length in the more distal 

 parts. Each theca lias an average length of about 2 mm. 



Remnrl-x. — All known British specimens which most closely resemble Hall's D. 

 iiidentus are badly preserved, and while the details of the proximal end can often 

 be made out, the characters of the thecae in the distal parts of the stipes are 

 generally obscure. So far as can be made out, there are more thecae in the same 

 unit of length than in Hall's species, and the specimens are smaller ; but taking 

 into account the conditions under which these fossils are found both in the l^ake 

 district and S. Wales, it is possible that they have been affected by cleavage, 

 and are therefore not normal. In many cases in the specimens from the Lake 

 district little can be made out except the general shape, but this appears to 

 agree so closely with that of Hall's species that they are here provisionally i-eferred 

 to it. 



Affinifif'S. — 1)., cf. indentvH resembles VA nanus in many particulars, but is 

 longer, and has fewer tliecae in the same unit of length. 



Horizon and Localities. — Upper Arenig — Lower Llandeilo. LaJce District : 

 Outerside ; Glenderamakin River; the Dodd, Skiddaw; Mosedale Beck, near 

 Troutl^eck ; Thornship Beck. St. ]>a rid' s District : Abereiddy Bay. 



Associates, etc. — The species occurs most abundantly in the Lake district, 

 associated with D. nanus; it also occurs in S. Wales at Abereiddy Bay at a 

 slightly higher horizon, associated with D. Murchisoni and its var. ijeminus, and 

 witli the forms usually referred to DipJograptns foJiaceus and Cryptogra'ptvs tricornis. 



