AZYGOGRAPTUS. 97 



Azygograptus coelebs, Lapworth. Plate XIII, figs. 4 n, h. 



1880. Azygograptus ccelvhs, Lapworth, Aun. Mag. Nat. Hist. [5], vol. v, p. 150, pi. v, figs. 16 a — c. 

 1898. Azygograptus coelebs, Elles, Quart. Joarn. Geol. Soc, vol. liv, p. 514. 



Stipes very slightly curved, 1'5 to 5 cm. in length and of uniform width of 

 about "5 mm., apparently growing out from the major extremity of a small 

 but relatively broad sicula in a direction perpendicular to its long axis. 

 Thecse ten in 10 mm., narrow tubes of uniform width, seven times as long 

 as wide, inclined at 15°, in contact for more than half their length near the 

 sicula, but with overlap diminishing distally ; outer walls with slight double 

 curvature. Apertural margins acute, straight, facing slightly inward. 

 Descriptio7i. — The stipes may be as long as 5 cm. ; they occur, however, more 

 commonly in a fragmentary condition not exceeding 1*5 cm. in length. 



The sicula is small and broad, but is nevertheless 



Fig. ^o7 a.-^A^y^ograptus cwiehs, ^^^-^^ couspicuous ; it mcasurcs about 'O mm. in 



length, and is considerably shorter and wider than 



that of Az. Lapworthi. The thread-like virgula 



Type specimen, showing details of growiug from the apcx of the sicula can occasionally 



proximal end in relief. Figured i flpfppfprl 

 Lapworth, 'Ann. and Mag. Nat. '^'^ ueieoueu. 



g^rgiS'^c^'i;^^^^^^^^ The earliest theca generally appears to arise 



close to the aperture of the sicula, but in well- 

 preserved specimens it can be seen that the actual point of origin is near its apex, 

 and that throughout its earliest period of growth the theca is closely appressed to 

 one side of the sicula, but after reaching the apertural region it takes a sudden 

 curve outward, and all the thecsB subsequently developed are straight and 

 practically horizontal. 



The average length of each mature theca is 

 Fio.ro7i,-Azyg^ojp-aptusc,,iehs, ^^^^^^^ ^ mm., and even the earliest formed ones 



appear to be of the same length. The amount of 



'^.'^>^--p^£:-"y^^s^ overlap decreases from one half to two thirds at the 



Distal thecal. Enhirgement of PI. XIII, proximal end to a quarter towards the distal end. 



The thecse show an approach to the Leptograptid ' 

 type both in the form of their apertures and in the slight double curvature of their 

 walls. 



Horizon and Locality. — Llanvirn, Upper Skiddaw Slates (Ellergill beds). 

 Lake District : Ellergill. 



Associates, etc. — Up to the present time Az. coeleJjs has only been recorded from 

 the Skiddaw Slates, and is apparently confined to the highest beds of that series, 

 where it occurs in association with TJiplog. clentatus ; l)ut it is alwa^'S rather rare. 



