44 



BRITISH GRAPTOLITES. 



Holywell Burn ; Hogstow Burn ; Stream west of Venus Bank ; quarter mile 

 north-east Knot Moor ; Leigh Quarry ; Snailbeach ; Stream five sixths mile 

 north-west Hope Church, etc. etc. lFc//p.s' — Merionethshire : Taihirion ; Carnarvou- 

 shire : Pont Seiont ; Penarfynydd Farm, Rliiw ; Porth Llawenan ; PembroJieshivr : 

 Porth-hayog, Ramsey Island ; Llanvirn Quarry ; Abereiddy Bay ; A^Tiitland. 



Associates, etc. — It occurs in association with D. patulus, I), affinis, D. acutideKs, 

 D. nanus, I). Nicholsoni, Glossogra'ptus ciliatus, and Diplogrctptns dentatus. 



It is often found in relief in great perfection, and good specimens are 

 in the collections of the Geological Survey of Great Britain and Ireland, the 

 Woodwardian Museum, the British Museum (Xat. Hist.), and the private collections 

 of PostletliAvaite, Lapworth, Nicholson, and the Authors. 



Didymograptus amplus, sp. nov. Plate IV, figs. 3 a- 



Stipes rigid, from o"8 to /"Gem. in length, curved at the commencement, but soon 



becoming straight, and diverging so as to include between them angles of 



20° — 2o° ; originally narrow, but widening continuously and rapidly up to a 



maxinnnn of 6"4 mm. Sicula long. Thecae eight to nine in 10 mm., 



inclined at 85° — 40°, free one fifth their length. Apertural margins normal, 



concave, mucronate. 



Description. — The stipes are very narrow at their origin in proportion to the 



width which they subsequently attain ; at first they measure only 1 mm., but they 



widen with increasing rapidity to 5 — nun., and this rapid increase in breadth is 



characteristic of the species, as is also the straight, rigid character of the dorsal 



walls. A slight diminution in width takes place at the extreme end of the stipes, 



owing to the incomplete development of the thecae. 



The sicula is conspicuously long (4 mm.) ; it is 

 narrow for the greater part of its length, but widens 

 somewhat abruptly near the aperture. Th. 1^ 

 appears to originate about midway betAveen the 

 aperture and apex of the sicula, but rather nearer 

 the former ; it groAvs outAvard and downwai'd 

 leaving the sicula free as usual on the left of its 

 aperture (obverse \\e^\) ; the crossing canal is thick, 

 and somcAvhat oblique ; the second tlieca is unusually 

 long; it measures 2 mm. in length, and the aperture 

 of th. 1' only reaches a point midAvay along its 

 length. There is a slight want of symmetry about the proximal end as a whole. 



The length of the thecfe is very different in different parts of the stipes : in 

 the initial region it is about 2 mm., and the thecae are tAvice as long as 



Fig. 27. 



- Didymograptus ampliia, 

 sp. nov. 



Proximal end, reverse view. Aber- 

 eiddy Bay. Coll. E. M. R. Wood. 



