Yol. 56.] FORMATION AND ITS GKAPTOLTTE-FATJNA. 475 



tubes, adult ones 1*7 mm. (-07 inch) in length and 3| times as long as 

 wide. At the proximal end the thecae are merely in contact ; distally 

 they overlap for not quite half their length. They are inclined to the 

 axis at an angle of 35° to 45°. Outer free wall rather deeply excavated 

 just above the aperture of the theca below, then expanding somewhat, 

 and again contracting slightly at the aperture, which is markedly 

 concave. The upper interthecal wall of each theca is continued as 

 a long flexible spine '63 mm. ("025 inch) long, generally curving 

 slightly over the aperture. 



This species is very characteristic of the Lower Ludlow, and is 

 readily recognized by its (a) small size, (6) thecal spines, and (c) gre- 

 garious habit, occurring as it does in great numbers on a slab 

 unassociated with other species. As in all other spinose forms, the 

 position of the spine varies considerably under different conditions 

 of preservation. In forms preserved in perfect profile it is clear 

 that the spine arises from the upper interthecal wall. In com- 

 pressed forms it seems to arise some little distance up the outer 

 wall of the theca next above,, but this appearance is deceptive. 

 Sometimes the aperture appears very narrow, and then the position 

 of the spine does not differ in any way from that of the spine of 

 Monograptus chimcera var. Saliveyi in a similar aspect. 



M. leintwardinensis has not been described from abroad, but, as 

 was pointed out on p. 473, Prof. Freeh's figure of M. uncinatus from 

 Scania may be that of a Swedish form referable to this species. 



Poreign Localities. — Djurrod in Scania? 



British Localities. — Ludlow district (Leintwardine, Church 

 Hill, Adferton ? Trippleton ? Aymestry, Vinnall) ; Broxton and 

 Burton; Long Mountain (Llettygynfach) ; Builth district (Aberedw) ; 

 Presteign, Old Ptadnor; Dee Valley (Llantisilio Road and Pen-y- 

 Vivod) ; Lake District ? 



Horizon. — M. leintwardinensis is the characteristic zone-fossil 

 of the highest beds of the Lower Ludlow, and ranges up into the 

 Aymestry Limestone. 



Associates. — It has not yet been found in association with 

 any other graptolite. 



Tar. incipiens, nov. (PI. XXY, figs. 22 a & 22 b.) 

 This variety agrees with the typical M. leintwardinensis in 



(1) The presence of the typical apertural spines in some of the thecas ; and 



(2) The number of thecae to the inch. 



It is distinguished from it by the following peculiarities : — 



(1) Polypary wider, the maximum width being 2 to 23 mm. (-08 to '09 



inch) and somewhat longer ; 



(2) Sicula broader, being '42 mm. ( - 016 inch) in diameter, and rarely more 



than 4i times as long as wide ; 



(3) The proximal thecae are provided with spines similar to those of 



M. leintwardinensis, but the distal thecaa have no spines, and are at 

 least 4 times as long as wide ; and 



(4) The adult thecae overlap for a half to three quarters of their length. 



