DTDYMOGRAPTUS. 21 



Affinities. — ]J. sKjjn-.stes appears to differ from all other forms in tlie character- 

 istic curvature of the stipes, and the rapidity with Avhich they increase in width. 



Horizon and Lonilitii^H. — Llandeilo, Upper (Glen- 



FiG. lie. — Bklyinograptus superstes, i m \ 

 Lapworth. Kllllj. 



Moffat iJi.strict : Birnock ; Hawkwood Burn, 



Ci;"'- -■' •&."'t2V^ W -V;> «;'- 





.55-"-"?".'*^ ;i^:> .^^--^^t? Abine'ton ; Morrach Bay : Portpatrick ; Tottlehams 



i^^^^'^iV"^^/§--f'^^> ) Burn; Castle DouQ'las. Oo. Doint and Co. Artnatih : 



Bally grot ; Oraigavad ; Ballymony, Hollywood, 

 Distal theea^^E,UalJem«ltof part of Poyntzpass. St. Dovid's District: Abcreiddy Bay. 



iShrop.sJt/ire : Spy Burn. 



Associates, etc. — 1). superstes is best knowni from the Glenkiln Shales of S. 

 Scotland, where it occurs associated with D. serratvlns, Cceaograptus (jracllis, 

 Leptograpttis sp., Bicellograptus Mofatensis, D. sextans, Dicranograptns ramosns, 

 D. tardiusculus, Diplograptus himucronatus, D. eaghjphns, Cryptograptus tricornis, 

 Glossog rapt lis cUiatus, and Clathrograptus cuneiformis. At Abereiddy Bay it occurs 

 associated with Didijmograptus Mvrchisoni, I), euodus, and various Diplograptidae. 



The best specimens are in Lapworth's collection, and in those of the Scotch and 

 Irish Greological Surveys ; there are also some in Swanston's collection. The type 

 specimen (PL I, fig. V) a) is in Lapworth's collection. 



Didymograptus euodus, Lapworth. Plate I, figs. 10 <t, h. 



187.5. Didynio(jraj)fHS euodus, Lapworth, Quart. Jonrn. Geol. Soc, vol. xxxi, p. 645, pi. xxxv, figs. 

 1 ft— c. 



Stipes several cm. in length, narrow at origin, but gradually increasing 

 throuofhout their length to a maximum of about 2*-l< mm., diveraine" from 

 the sicula at a primary angle of 150°, but after a short distance curving 

 back and running horizontally. Thecae seven to eight in 10 mm., peculiai" in 

 form, having slight double curvature in their outer walls ; inclined at about 

 ■]0°, five times as long as wide, and free for half their length. Apertural 

 margins normal, concave, broadly mucronate. 

 Description . — The stipes are narrow at their origin, and exhibit marked curva- 

 ture ; they measure only •(} mm. in width at first, but increase steadily and almost 

 imperceptibly up to a maximum of about 2*4 mm. This maximum width is not 

 attained till a length of about 15 cm. has been reached, so that when completely 

 developed the species must have been 30 cm. or more in length. Examples showing 

 the proximal end in a fair state of preservation are rare, though fragments of 

 stipes are fairly abundant at a certain horizon. 



The sicula is wide in proportion to its length, which does not exceed 1*05 mm. ; 



