148 



BRITISH GRAPTOLITES. 



Figs. 91 a and b. — Bicellograpttus patu 

 losus, Lapw. 



f* 3 



JS 





a. Proximal ond showing oblique posi- 



tion of sicula. On same slab as PL 

 XXI, fig. 5 e. 



b. Proximal end, showing complete 



sicula. Enlargement of part of PI. 

 XXI, fiff. 5 b. 



Fius. 91 c, d, and c— Dicellograptus patulosus, 

 Lapw. 



•4 mm. to 1 mm., maintain this width for the remainder of their length. The angle 

 of divergence is very variable, as is also the amount of curvature. In some 



specimens there is a persistent convex curvature 

 from their proximal to their distal ends ; in others 

 the curvature is hardly perceptible ; while in others, 

 again, it may be slightly concave. 



The sicula when perfect is very long, measuring 

 2" 5 — 3 mm. ; its apex is, however, frequently broken 

 off either partially or entirely, though its apertural 

 spine is more frequently seen, and is stout and of 

 considerable length. The sicula is rarely shown in 

 its normal position with respect to the dorsal angle 

 of the stipes, but is bent over to one side or the other 

 — sometimes, indeed, lying right across one or other 

 of the stipes, and being occasionally united to the 

 nearest stipe by a distinct membranous film. 

 The thecae are eminently characteristic, and differ essentially from those of the 

 majority of Dicellograpti in the fact that they narrow towards their aperture, which is 



itself oblique and directed inwards. There is 

 but slight introtorsion of the apertural portion. 

 A very small fraction only of the apertural 

 margin lies outside the line formed by the 

 ventral edge of the polypary ; hence the thecal 

 border has a very smooth appearance. The 

 excavation is both shallow and narrow, and 

 occupies about one third the width of the stipe, 

 and a very small fraction of the length of the 

 theca. 



Affinities. — D. patulosus bears some slight 

 resemblance to I). Forchammeri in the form 

 of the axil, but differs from it in the characters 

 of the thecas. From all other Dicettogra/pti its 

 habit is sufficient to distinguish it. 



Horizon and Localities. — Glenkiln Shales. 

 8. Scotland. : Dobb's Linn ; Craigmichan Scaurs ; Glenkiln Burn ; Belcraig 

 Burn, etc. Radnorshire : Builth Road ; Wellfield. 



Associates, etc. — I), patulosus occurs in great abundance in a single zone in the 

 Glenkiln Shales near their upper limit, associated with various Diplograpti, Dicranog. 

 ziczac, Thamnogra/ptus, sp., etc. 



There are good specimens in the Sedgwick Museum and in the private col- 

 lections of Lapworth and the Authors. 



: >i_fi^ 



c, Proximal thecse, showing introtorsion of 

 apertural region. Dobb's Linn, Glenkiln 

 Shales. Coll. Wood. 



</. Distal thecae, showing characteristic narrow- 

 ing towards aperture. Specimens on same 

 slab as PL XXI, figs. 5 a and 5 b. 



c. Scalar if orm view of thecee. Rein Gill, 

 Wandel Water; Glenkiln Shales. Coll. 

 Geol. Survey of Scotland. 



