114 



BRITISH GRAPTOLITES. 



-Lcptii'iriiiith 

 MS. 



validus, Lapw. 



Distal thecae in full relief. Enlargement 

 of PI. XVI, Eg. 1 c. 



The apertures of the proximal theca? are slightly mucronate. The thecae in the 

 maturer parts of the stipes have an average length 

 of 2 mm., their free outer walls are straight, and 

 the apertures are wide. 



Affinities.- — L. validus is allied to L. fiaccidus, but 

 differs in the mode of growth of the stipes, and in 

 the characters of the thecal apertures, which are 

 typically entire even at the proximal end. 



Horizon and Localities. — Upper Llandeilo (Rorrington Flags). Glenkiln Shales ? 

 Shropshire: Spy Burn. S.Scotland: Glenkiln Burn ? 



Associates, etc. — L. validus is a very common fossil at certain horizons, and in 

 S. Shropshire it occurs rarely in the Nemagraptus {Coenograptus) beds, and in pro- 

 fusion in the beds immediately overlying them at Spy Burn, the specimens being 

 usually preserved in full or half relief. It is associated with Didymog. superstes, 

 Dicellog. sp., L. latus. Good specimens are in the collections of Lapworth, H.M. 

 Geological Survey, and the Woodwardian (Sedgwick) Museum. 



Var. incisus, Lapworth MS. Plate XVI, figs. 2 a, b. 



Var. incisus agrees with L. validus in general form, but differs in having less 

 closely set thecae, and in the wide and oblique character of the thecal apertures. 

 The sicula also is slightly longer than in the typical form. 



The stipes are always slender, and commonly somewhat rigid, though they may 

 be very slightly flexed ; they have a width of about "4 mm. at the proximal end, 

 and widen very gradually up to a breadth of '7 mm. 



The sicula is conspicuous, it has a length of 2 mm., and its aperture is entirely 

 concealed in the reverse aspect of the polypary. The first theca (th. I 1 ) originates 



basally, and grows at once obliquely outward and 

 slightly downward. The crossing canals are prac- 

 tically horizontal, so that the apertures of the thecae 

 on the primary and secondary stipes come to lie at 

 much the same level and distance from the sicula, 

 and hence the appearance at the proximal end is 

 very symmetrical . 



The thecae number nine to eight in 10 mm., 

 though there may be as many as ten close to the 

 sicula; each theca is inclined at 12°, has an average 

 length of about 2 mm., a uniform width of about 

 •:> mm., and is free from two-thirds to one-half of its 

 margins are slightly concave when compressed, subniu- 



Fi<;. 69 a. — Leptograptus validus, var. 

 incisus, Lapw. MS. 



aspect. Enlargement of part 

 of PL XVI, fisr. 2 a. 



Fio. 69b. -Leptograptus validus,xs 

 incisus, Lapw. MS. 



Distal thecae. Enlargemenl of part of 

 PL Ml, ag. 2b. 



extent. The apertural 



