36 



BRITISH GEAPTOLITES. 



Figs. 23 a and b. — Didymograptus 

 deflexus, sp. nov. 



rapidly to a width of 1 mm. near the bend ; in the largest specimens the Tndtli 

 may be as much as 1*5 mm., but the smaller breadth is the more usual. As in 

 D. v-fractus, there is great variation as regards the length of the V part and 

 the subsequent direction taken by the stipes. In some specimens the V part is 

 narrow and rather long ; in others it is small, and the stipes after the bend are 

 exceedingly long in proportion ; while in others again the initial angle of 

 divergence is greater, and the change in direction less abrupt. Some forms 

 indeed approach very nearly to Tullberg's D. vaciUaiis, but the stipes in that 

 species are of uniform width throughout, which is never the case in JJ. rlcflexus. 



The sicula is long and narrow ; it attains a 

 length of 1'6 mm. exclusive of the prolongation 

 from its apex (nema). The sicula is not placed 

 symmetrically with regard to the stipes ; it is nearer 

 the stipe bearing the second thecal series. The 

 first theca (th. 1') appears to originate from the 

 sicula some distance above its aperture ; it groAvs 

 at first away from the sicula in a horizontal direction, 

 and thus in the obverse aspect the sicula is seen 

 to be free on the left side near the aperture. After 

 growing horizontally it curves downwards. Viewing 

 the polypary in the reverse aspect, theca 1" is seen 

 to l)e closely appressed to the apertural part of 

 the sicula ; the crossing canal is also visible, and 

 is narrow and runs somewhat obliquely. 

 The thecge in the initial part of the polypary are about 1-20 mm. long; they 

 have their walls concavely curved, ])ut after about two or three thecje are formed 

 this concave curvature begins to give place gradually to a slight convex curvature. 

 The thecsD thus curve away from each other, and the general direction of the stipe 

 is changed. The thecal walls in the distal portion of the stipes are nearly straight ; 

 the thecae have a length of 1*6 mm., and are about three times as long as wide. 



Affliiitie.'i. — This species was originally included with Salter's D. v-fractiis 

 (Elles, ' Quart. Journ. Geol. Soc.,' vol. liv, p. 508), but an examination of additional 

 specimens shows that the smaller form is not merely a young individual, but 

 belongs to a distinct species. 



The general shape of the polypary resembles that of V. r-fractus, but the V 

 part is shorter in proportion to the size of the polypary, and the whole is more 

 slender and graceful. 



Horizon and Localities. — Arenig (Middle Skiddaw Slates). 



Lake District : New Brow Quarry, Upper Lorton ; Dodd, Brackenthwaite ; 

 Barf, near Keswick ; Brunstock Scar. 



Associates, etc. — T). def exits has, up to the present time, been recorded from 



a. Proximal end in relief, obverse 



view. Enlargement of part of 

 PI. II, fig. 12 6. 



b. Proximal end, cast, reverse view. 



Enlargement of part of PI. II, 

 fig. 12 a. 



