MONOGRAPTUS. 387 



ThecfB twelve to ten in 10 mm. ; of two types, those of the proximal 

 portion with a tendency to ogee carvatnre and with conspicuously retro- 

 verted apertural region ; those of distal portion simple tubes with even and 

 somewhat everted apertnral margins ; overlapping fully one-half their length. 

 Description. — The polypary is usually rather smaller in size than that of either 

 M. revolntn.-i or its variety prsecnrsor and shows more abrupt involution of the 

 proximal extremity ; it is also more robust in the proximal portion than either 

 of those forms. 



The sicula is small Init conspicuous ; it measures about 1 mm. in length and 



the polypary has a breadth of nearly 



Figs. 256 a and h. — Monograptus difformis, Tornquish . '. . 



•3 mm. in its immediate neijj'hbour- 



\\\ hood. 



/?^ I The proximal thecas show a further 



^ i development of the tendency to retro- 



^\ _ \3 I ^ version of the apertural region and 



\ !i :\''i V fi^l^y one-third of the tlieca is isolate ; 



/,: '1 X ,f \ distally, however, the thecae gradually 



'^'^'i Yf} » lose the curvature of their walls and 



'*'^\ fi, vN " j I become simple parallel-sided tnbes 



' (i^\ // ^\ k with even and slightly everted aper- 



*^^> «^~ — r.n' :^^'%-;r^ iv^ tural margins. In the proximal thecae 



^ ^' the amount of overlap is very slight, 



T, • 1 ,.■ » ., , ^ . i. r . but this steadily increases in amount 



a. Proximal portion ot the polypary. Enlargement of pai-t ■^ 



ofPi XXXVIII fig- 4 a. .,,,,,„ until distally it is fully one-half of 



0. Proximal portion ot polypary, showing sievila ; doubtfully '' "^ 



referable to this species. Enlargement of part of tllC entire lenSTth of the tllCCa. 

 PI. XXXVIII, fig. 4 (i. , . . 



Affliiities. — Monog. difformis pre- 

 sents some points of resemblance to M. revolnfus and its variety yraecursor. It 

 may, however, be readily separated from M. revolatus by the more robust 

 character of the proximal end and the greater retroversion of the proximal thecffi ; 

 from var. iwxcursor, however, it differs mainly in the more robust character of the 

 proximal portion of the polypary, the retroversion of the proximal thecae being 

 very similar in the two forms. 



Horizon and Localities. — Llandovery, Birkhill Shales (zone of Monog. gregarlus). 



8. Scotland : Dobb's Linn. C. Wales : Rheidol Grorge. N. Wales : Llany- 

 stwmdwy. 



Associates, etc. — Monog. difformis apparently occurs in the lower part of the 

 zone of M. gregarriis, associated with Monog. fiinbriatus and M. revolatus, var. 

 austerus. It does not seem to be a common fossil. 



Collections.— Jones, Fearnsides, Lapworth, and the Authors. 



