DIDYMOaRAPTUS. 



33 







Characters of Group of D. 



affinis. 







D. affinis. 



D. gracilU. 



Narrow, 

 rigid, hori- 

 zontal 



Z). acutidens. 



D.Nichohoni. 



D. serratulus. 



2>. simulans. 



D. cf.filiformis 



Form of stipe . Narrow, 

 rigid, 

 straight 



Narrow, 

 rigid, 

 nearly 



straight 



Narrow, 



rigid, 

 straight 



Narrow, 



rigid, 



straight 



Narrow, 

 rigid, 

 curved 



Narrow, 



rigid, 

 straight 



Angle of diver- 



90°— 150° 



180° 



160° 



110°— 130° 



120°— 130° 



115°-160° 



90° 



gence 

















M a X i m n m 

 width 



■(3 mm. 



'5 mm. 



•63-1-5 

 mm. 



1 mm. 



1 mm. 



1-4 mm. 



■5 mm. 



1 



Length of 

 sicula 



•8 mm. 



1-2 mm. 



13 mm. 



18 mm. 



2 mm. 



15 mm. 



21 mm. [ 



Origin of 



stipes 



Siiboral 



Suboral 

 (medial) 



Suboral 

 (medial) 



Suboral 



Suboral 



Suboral 



Apical 



No. of tliecae in 

 10 mm. 



8 



7 



11—13 



10—11 



7-8 



13-14 



7 



1 



Inclination . . 



15°— 20° 



15° 



15°— 17° 



25°— 30° 25° 



30° 



20° 



Overlap . . . 



Very small 



Very small 



Contact to \ 



Contact to ^ Contact to \ 



Contact to 1 



Very small 



1 



Deflexed Semes. 



Didymograpti witli flexed stipes diverging down-ward, in wliicli tlie initial 

 ano-le of divers-ence is less tlian 180°. 



Group IV. — Type T). r-fracfui^. 



Didymogra|)ti in wliicli the stipes grow outward and downward; they 

 originate above the aperture of the sicula, and are at first concavely and then 

 convexlv curved. The thecf^ are inclined at moderate ano-les, and the amount 

 of overlap is considerable. 



Didymograptus v-fractus, Salter. Plate II, figs. 10 a, h. 



1863. Didymograpsus v-fractas, Salter, Quart. Journ. Geol. Soc, vol. xi.x, p. 137, fig. 18 c. 



1868. Diclymo(jrapsH8 v-fractnit, Nicholson, Quart. Journ. Geol. Soc, vol. xxiv, p. 134. 



1895. Dkhjmograptus v-fradus, Perner, Grap. de Bohcme, pt. 2, p. 24, pi. v, figs. 15, 16 ; pi. vii, 



figs. 1, 2. 

 1898. Didymograptus r-j'ractnf, Elles (pars), Quart. Journ. Geol. Soc, vol. liv, p. 508, noti figs. 



25—28. 



5 



