412 



BRITISH GlIAPTOLITES. 



Fig. 277. -Monogmpius vomennus, var. exccecls 1 'G mill., wliile tlic sicula is sliort, measuring 



gracilis, nov. " 



1"2 mm. in lengtli. The tliecse number thirteen in 



10 mm. 



Horizon and Localities. — Wenlock Shales (zone 



of Gi/rtog. Murclilsovi). 



Wales : Pencerrig, near Bnilth, Scotland : Ric- 

 kV carton. 



Kf Associates, etc.' — So far as our present knowledge 



(p extends var. gy'acilis is confined to the basal zone of 



I the Wenlock Shales. 



' Collections.— lJi\'^^^'Ovt\\ and the Authors. 



Proximal end, showing sicula. Castle 

 Crab, nr. Builth ; Wenlock Shales. 

 Coll. EUes. 



Var. crenulatus (Tcirnqnist). 



Plate XLI, figs. 4 a- 



1881. Monofjrajjtvs crenulatus, Tornquist, Geol. Foren. Forliandl., Bd. v, p. 438, pi. 17, fig. 4. 

 1892. Monograptus cremdatiis, Tornquist, Siljansoinradels Graptol., ii,p. 11, pi. i, figs. 12 — 16. 

 1900. Monograptus vomerinus, var. y, Elles, Quart. Jouru. Greol. Soc, vol. Ivi, p. 405, fig, 15. 



Figs. 27H a-e.—Monogroi)lus vomerinus, var. 

 crenulatus (Tornquist). 



ah c d c 



a. Proximal end, sliowing sicula. Tarannon 

 River, near Dolgavi Farm ; Dolgau Beds. 

 Coll. Wood. 



h. Adult thecffi : in relief. Enlargement of 

 part of PI. XLI, fig. 4 b. 



c. Adult theca3 ; preserved as a cast. Part of 



same specimen as Fig. ^78 h. 



d. Adult thecae ; preserved so that apertures 



are concealed. Enlargement of part of 

 specimen on same slab as Figs. 278 h and c. 



e. Specimen in relief, showing thecal apertures. 



Enlargement of part of PI. XLI, fig. 4 c. 



mount Road, Conway ; Tarannon 

 below Pen-y-graig, Llanbrynmair 

 of Lledcwm, Llanbrynmair, etc. 



In addition to the varieties of Moiiog. vome- 

 rinus enumerated above, there occurs at the 

 top of the Tarannon Shales and ranging thence 

 into the lowest Wenlock Beds, a characteristic 

 variety which is certainly their forerunner; 

 this has been regarded as a distinct species, 

 but it is best considered as a variant of the 

 typical M. vomerinus, in which the thecse are 

 more closely set in the proximal portion (thirteen 

 to ten in 10 mm.), and the a2:)ertural excavation 

 is smaller (one-fifth the total breadth of the 

 polypary). The proximal end is practically 

 straight ; the sicula has a length of 1'5 mm., but 

 unlike that of the typical form the first theca 

 is so short that the apex of the sicula reaches 

 to the level of the aperture of tli. 2. 



Horizon and Localities. — Gala- Tarannon 

 (zone of M. crenulatus). 



Wales : Benarth Wall, Conway ; Neckar- 

 River ; Afon laen, between Dolfach and bridge 

 ; Plasbach Stream, Llanbrynmair ; stream east 



