Yol. 56.] .FORMATION AND ITS GKAPTOLITE-FAUNA. 471 



British Localities. — Ludlow district (Elton Lane, Elton- 

 Ludlow Eoad ? ; Adferton ? ; Dudley (Sedgley Shales) ; Long Moun- 

 tain (Trefnant-Middletown Brook) ; Builth (Aberedw Hill). 



Horizon. — In Bohemia it occurs in the Limestone Ee 2, and 

 belongs, therefore, characteristically to the Lower Ludlow. In 

 Britain it is found in the zones of Monograptus Nilssoni and 

 M. scanicus, characteristically in the latter. 



Associates. — M. scanicus, M. chimcera, and M. Nilssoni. 



(c) Group 3. Type M. chimjera (Barr.). 



1. Proximal extremity of the form of that of the M.-colonus type. 



2. Thecal apertures provided with long spines. 



Monograptus chimjeba (Barr.). (PI. XXV, figs. 18a-18d.) 



1850. Grajptolithns chimcera, Barrande, ' Graptolites de Boheme' p. 52 & pi. iv, 

 figs. 34-35. 



Polyp ary. — 2*54 to 3*8 cm. (1 to 1*5 inch) long, straight 

 distally, but with a distinct dorsal eurvature for the first 5 mm. 

 (•2 inch) of its length. Increase in width most rapid for the first 

 five or six thecae, but generally slight throughout the whole length. 

 Width at the aperture of the first theca (exclusive of spines) = 

 generally about '89 mm. ("035 inch), while the maximum width of 

 the distal end (exclusive of spines) is 1*9 mm. (-075 inch). Virgula 

 produced slightly beyond the distal end. 



Proximal Extremity. — Sicula approximately 1*7 mm. (-066 

 inch) long, extending to about midway between the apertures of 

 the second and third thecae. Width at the aperture = "34 mm. 

 (•013 inch), hence the sicula is approximately 5 times as long as wide. 



Thecae. — Thirty-two to twenty-eight in the inch (thirteen to eleven 

 in 1 cm.), inclined to the axis at an angle of about 40° to 50°. 

 Straight broad tubes, fairly uniform in width throughout, provided 

 with a stout blunt spine arising from the aperture. This spine 

 has a maximum length of *63 mm. (*025 inch), and arises slightly 

 above the centre of the lateral wall of the aperture, though the 

 apparent position varies considerably in compressed specimens. 

 The proximal thecae are twice, and the distal thecae 4 times as long 

 as wide. The amount of overlap is about half of the whole length. 



I have referred this species provisionally to M. chimcera (Barr.), 

 since the type of thecae and position of the spine are similar in 

 the Bohemian and British forms. The Bohemian type-specimen, 

 however, is small, only 12-7 mm. (-5 inch) long, and is not well 

 preserved, and possibly a further study of more perfect specimens 

 may prove that the British form is a variety of it. No other species 

 resembles this closely, except M. Salweyi (Hopk.) and M. colonus, 

 Jaekel, and its affinities to these will be considered later. Numerous 

 small specimens occur in association with the adult forms at the 

 Elton-Ludlow Eoad locality (PI. XXV, fig. 18 d), which differ 

 somewhat in their general shape, but they may be only young 

 forms, and are not worthy of a varietal distinction. 



I have examined a large number of specimens in the hope of 



