Vol. 56.] FORMATION AND ITS GKAPTOLITE-PATJNA. 455 



8*9 to 10 cm. (3^ to 4 inches) and is somewhat broader. In all cases, 

 however, the shape of the thecseis the same, and it seems impossible 

 to separate the extreme types in the present state of our knowledge. 



One form belonging to the group typified by Monograptus dubius, 

 from the Lower Ludlow Eeds of the Ludlow district, has been figured 

 as M. serra, Hopk. ; but, after a careful examination of numerous 

 specimens, I find that I am unable to separate it from M. dubius, even 

 as a distinct variety. This may possibly be done when the characters 

 of M. dubius are more clearly defined. The slightly spinose 

 apertural denticle so characteristic of M. serra is equally well 

 marked in specimens of M. dubius from the Wenlock Shales of 

 Builth. The Bohemian form figured by Dr. Perner as M. dubius 1 

 also exhibits this character quite as distinctly. The original 

 figure of M. dubius given by Suess is a very indifferent one, but 

 in spite of this the graptolite appears to have been as a rule 

 correctly identified by British geologists. Dr. Perner has recently 

 refigured and described Suess's type-specimen, and the British forms 

 agree well with it. 



Foreign Localities. — Bohemia (Vyskocilka, Kuchelbad, 

 Kozel, Borek, etc.) ; Sweden (Bostanga, Tomarp, Tibarod) ; Harz 

 Mountains, etc. 



British Localities.' — Ludlow district (Elton Lane, Stormer 

 Hall, Elton-Lndlow Boad, etc.) ; Builth (Aberedw Hill, etc.) ; Long 

 Mountain (Glyn Brook, etc.) ; Lake District (Moughton) ; Southern 

 Scotland (Biccarton and Hindhope). 



Horizon. — Lower Ludlow Shales (zones of M. vulgaris, M. Nils- 

 soni. and M. scanieus). It also occurs in the Wenlock Shales. 



Associates. — M. Nilssoni, M. bohemicus, M. scanieus, M. cJii- 

 mcera var. Salweyi, M. uncinatus var. micropoma, M. varians 

 and its variet}* jpumilus, M. vulgaris. 



MONOGRAVTVS VULGABIS, Sp. n0V. (PI. XXV, fig. 2.) 



Polypary attaining a length of 5 to 10 cm. (2 to 4 inches) 

 or even exceeding that length. Straight at the proximal end, 

 except for a slight incurve of the first three or four thecse ; when 

 about half the length is reached the polypary curves gently, so that 

 the outer margin is slightly concave. Eorm of the polypary very 

 characteristic, recalling that of M. Hoemeri. Virgula prolonged for 

 a short distance distally. Width at the proximal end = about "76 mm. 

 (•03 inch), increasing to a maximum width of 2-54 mm. (-1 inch) at 

 the distal end. Increase in width most rapid for the first 12*7 or 

 19 mm. (-5 or -75 inch), at the rate of about *127 mm. (-005 inch) 

 for each theca ; after this the increase is more gradual until the 

 distal extremity is reached. 



Proximal Extremity. — Most characteristic, serving to dis- 

 tinguish this species readily from all others related to it. Sicula 

 about 2 mm. (-08 inch) long, '5 mm. (-02 inch) wide at the aper- 

 ture, hence only 4 times as long as wide ; inner wall of the 



1 'Etudes sur lee Graptolites de Boheme' pt. iii, sect, b (1899) pi. xiv, fig. 11. 



