270 BRITISH GRAPTOLTTES. 



sigmoid curvature so characteristic of those of the sub-genus Am/plexogra/ptus . The 

 free part of the ventral wall is straight and slightly inclined, and the excavation is 

 deep and oblique, but narrower than in A. perexcavatus. 



Lap worth notes the occasional presence of a " rudimentary proximal spine" 

 on each theca, but we have not been able to prove its existence with certainty. 



Affinities. — A. confertus is closely allied to Amplexog. perexcavatus, but it may 

 be distinguished by the smaller size and general form of the polypary, and by the 

 introverted and narrower apertural excavations. 



Horizon and Localities. — Lower Llanvirn (zone of Didymog. bifidus). 



Wales ; Porth-Hayog, Ramsey Island ; Lampeter Velfrey ; Llan Mill, near 

 Whitland ; Ffairfach Station, Llandeilo, etc. ; Pont Seiont, Carnarvonshire. 



Associates, etc. — Amplexog. confertus is a fairly common fossil in the zone of 

 Didymog. bifidus in North and South Wales. It occurs associated with I), bifidus, 

 D. artus, D. acutidens, and D. patulus. 



Collections. — Sedgwick Museum, Geological Survey of England and Wales, 

 Lap worth, and the Authors. 



Diplograptus (Amplexograptus) ccelatus (Lap worth). Plate XXXI, figs. 17 a — c. 



1875. Cliinacograjitus ccelatus, Lapwortli, Quart. Jouru. Geol. Soc, vol. xxxi, p. 655, pi. xxxv, fig. 8. 



Polypary 5 — 6 cm. or more in length, widening fairly rapidly to a maximum 

 breadth of 3*2 mm., and having parallel margins for the remainder of its 

 extent. Sicula unknown, virgella and virgula of considerable length. 

 Thecae long and slender, ten to eight in 10 mm. ; in the obverse aspect, 

 ventral wall sigmoid, apertural margins slightly undulate, situated in short 



Pio. m.-Anwiexograptus caiatus and shallow excavations occupying but a 



(Lapw -)- small fraction of the width of the polypary, 



and less than one fourth of the ventral 

 margin ; in the reverse aspect, denticle sharp 

 and angle of inclination high with respect to 

 the axis of the polypary. 

 Description. — The polypary is usually of con- 

 siderable extent; the proximal end is about 1 — 1*5 

 mm. broad, but the maximum width is generally 

 attained within the first cm. of its length and is 



Distal thecae, showing a typical Diplo- . , . ,. , . m , . , 



graptus appearance on the left side continued up to the distal extremity. 1 he virgula 



and a Climacograptus appearance • .-, -, -i -i • j n -iji • 1 



on the other. Enlargement of part is greatly prolonged distally, and there is also a very 



long proximal prolongation (? virgella), sometimes 

 as long as the polypary itself, which is thickened by a membrane for a distance of 

 2 — 3 mm. below the proximal end. 



