232 



BRITISH CiRAPTOLITES. 



Pias. 152 a, b, and c. — Orthograptus bel- 

 luhis, Tornq. 





is often prolonged for 8 mm. or more; it is, however, rarely completely preserved. 

 The overlap of the thecas is less in the initial than in the distal portion of the 



polypary, and the apertural margins appear to be 

 everted in specimens preserved in relief. No 

 septum is visible in either aspect. 



Affinities. — In the increase in the concavo-con- 

 vexity of the polypary 0. bellulus approaches the 

 Mesogra/pti ; indeed, distal fragments of Orthog. 

 bellulus closely resemble Mesog. moclestus in their 

 general characters, but have the thecas much more 

 closely set ; the long virgella and characters of the 

 thecal in the proximal region are, however, sufficient 

 to distinguish it when the complete specimen is 

 seen. 



Horizon and Localities. — Llandovery (Upper 

 Birkhill Shales) (zones of M. convolutus and M. 

 spinigerus). 



S. Scotland ; Dobb's Linn ; Belcraig Burn, etc. 

 Lake District : Skelgill. Wtdcs .- Llanystwmdwy ; 

 Rhayader ; Llanbrynmair. 



Associates, etc. — 0. bellulus is a fairly common 

 fossil in the Upper Birkhill Shales of S. Scotland, 



portion of sicula. Note absence where it OCCUrS associated with MoilOQ. SpilliacrilS, 

 of septal groove. Skelgill, Skelgill , , if f if > 



shales. Coil. Sedgwick Museum. M. convolutus, M. Glingani, M. lobiferus, Gejphalog. 



cometa, G. petalum and other forms. It also 

 occurs with a similar fauna at Skelgill. 



Collections. — Sedgwick Museum, British Museum (Natural History), Fearn- 

 sides, Lapworth, and the Authors. 



•> 











a. Proximal end, showing long virgella. 



Belcraig Burn, Birkhill Shales. 

 Coll. Wood. 



b. Proximal end, showing form of thecoe. 



Dobb's Linn., Birkhill Shales (If. 

 Clingani beds). Coll. Lapworth. 



c. Proximal end in relief, showing small 



Diplograptus (Orthograptus) mutabilis, sp. nov. Plate XXIX, figs. 1 a— d. 



Polypary large, 4 — 5 cm. in length, widening rapidly from origin till the 

 maximum breadth 3 — 3'5 mm. is attained, thence margins sub-parallel. 

 Sicula large. Thecae twelve to nine in 10 mm., overlapping one half to 

 two thirds their length, apertnral margins slightly lobate, with fairly 

 conspicuous rim or flange. 

 Description. — The polypary is widest close to the proximal end, the increase 

 taking place within 1 cm. of the proximal end, and attaining a breadth of 

 3 — 3 - 5 mm. from an initial width of 1*5 mm. ; subsequently there is slight diminu- 

 tion, and the ventral margins arc then almost straight and parallel for the 



