MONOGRAPTUS. 



147 



Figs. 307 a and 6. — Mo nog rapt us testis, var. 

 inornatus. Elles. 



which are characteristic of the British form; hence the latter is here provisionally 

 regarded as a distinct variety. 



The polypary is small, measuring only about 1 cm. in the specimens known, 



and has a maximum breadth of '2 mm. 

 The thecae number fifteen in 10 mm., 

 and have conspicuously retroverted 

 apertural regions, and, as above men- 

 tioned, the apertural margin appears to 

 %p> .^.r^. "i , De devoid of long spines. 



Horizon and Localities. — Upper Wenlock 

 Shales (zone of Gyrtog. Lundgreni). 

 ^ Shropshire : Trewern Brook, near Middle- 



y priodon-type of thecae. town ; Garbett's Hall, near Middletown ; Ackley 

 Lane, Long Mountain. 



Associates, etc. — Monog. testis var. inornatus 

 appears to be a rare fossil, and seems to be 

 confined to the Gijrtog. Lundgreni zone, where it occurs in association with the 

 zone fossil, M. Flemingii var. compactus and M. dubius. 

 Collections. — Professor W. "W. Watts, and the Authors. 



v-T/ <( /j*v, 



^i.1 -..-¥ .KM-*' 



Enlargement of part of PI. XLIV, fig. 7 a. 

 b. Theeffl showing indications of apertural 

 spines. Enlargement of part of PL XLIV, 

 fig-. 7 b. 



Gkoup V. 



Monograpti in which the mature thecae are tubes with the whole apertural region 

 coiled into a definite lobe. 



In the Monograpti included in the present group the isolation and retroversion 

 of the apertural region of the tlieca are still further intensified. The theca in the 

 course of its development becomes as it were folded back upon itself, its axis 

 curving through a thecal angle exceeding 180°, and the whole of the apertural 

 region is rolled into a distinct coil or " lobe." This may be coiled tightly 

 as in M. Jcnoclcensis, or loosely as in M. runcinatus. 



In all cases there is considerable torsion of the theca, so that after compression, 

 what seem to the eye to be shortened or lengthened appearances of the thecae 

 are often presented, giving the polypary a very different look in the two cases. 

 These diverse appearances seem sometimes to have been interpreted as belong- 

 ing to distinct species. 



Considerable differences exist in the amount of the thecal length which is 

 isolate (/. e. prolonged beyond the final point of overlap), and also in the proportion 

 of this amount which is involved in the lobe itself ; distinctions which when constant 

 appear to constitute characters of specific value. Again, the transverse diameter of 

 the lobe in some species is small compared with the breadth of the polypary as a 



59 



