12 BEITISH (IRAPTOLITES. 



Didymograptus uniformis, sp. nov. Plate I, figs. 3 (?) and 4. 



Stipes 5 cm. or more in length ; bent at tlieir origin into a small inverted V, 

 but running later in an approximately horizontal direction, ha^dng a 

 uniform width (1'6 mm.) for the greater part of their length. Sicula con- 

 spicuous. Thecge eleven in 10 mm., inclined at 30°, three times as long as 

 wide, in contact one half to two thirds their length. Apertural margins 

 normal, straight. 

 Description. — The stipes are "9 mm. wide at their origin ; they increase in the V 

 part up to 1*3 mm., and this width is maintained for the remainder of their length, 

 which may be as much as 5 cm. This uniform width is especially characteristic 

 of the horizontal portions of the stipes ; the V part is about 6 mm. in extent. 



The sicula measures 1*8 mm. in length, and the first theca appears to develop 

 from the apical region, and growing straight downward beyond the aperture of the 

 sicula has its ventral wall closely appressed to the sicula. This direction of growth 

 parallel to the sicula is also followed by all the earliest developed thecse, and their 

 ventral margins are straight. 



The later tliecfe are equal in length to the sicula ; 



Figs. 6a and b- Didymograptus uni- ^J^g ^^^ incHued at a COUStaut angle of 30°. TheV 



_/07'))iis, sp. nov. 'J o J 



are in contact for half their length in the proximal 

 regions of the stipes, but this amount increases to 

 nearly two thirds in the more distal parts. There 

 is a slight sigmoid curvature of the outer wall, each 

 thecal wall showing slight concavity in its initial 



Proximal end preserved mainly as a . i ■ i i T i 



cast, obverse view. Enlargement region, whicli changes to slight coiivexity near the 



of part of PI. I, fig. 4. " ^ 



aperture. 



Affinities. — D. uniformis approaches most nearly 



in shape to /). nitidus and D. simulans ; from 

 D. nitidus it may be distinguished by its larger sicula, 



h. Distal thecse of same, in full relief, ,, , „,, ., , ,,, .„ 



enlarged. the character or the proximal end, and the unitorm 



width ; from D. simulans it differs in the characters 

 of the proximal end and those of the thecae. 



Numerous examples of a form of Didymograptus on a slab in the possession of 

 Mr. Christopherson from the Skiddaw Slates at Raulnay may be provisionally 

 referred to this species. They agree with D. uniformis as regards — 



(1) the uniform width of the polypary, 



(2) the proximal end, 



(3) the number and form of the thecse. 



