MONOGRAPTUS. 487 



Affinities. — The long slender polyparj of Monog. cf. cJongatuti, with its irregular 

 flexure and characteristic thecce, is distinctive. Fragments, however, somewhat 

 resemble those of M. intermedia^ as respects the general characters of the thecse, 

 but the lobation of the apertural terminations is more pronounced. 



Horizon and Localities. — Llandovery (zones of 31. gregarins and M. convolttins). 



WaJes : Llanystwmdwy, near Criccieth ; Rheidol Gorge, 440 yds. S.S.B. of 

 Bryn-chwith Farm, Pont Erwyd ; 10 yds. up stream from crest of anticline, N. 

 of Fuches-gau Farm, Pont Erwyd. 



Associates, etc. — M. cf. elongatus occurs at the top of the zone of M. gregarins 

 associated with M. argutns, M. leptotheea and M. lohiferiix, and in the zone of M. 

 convolutns immediately above with M. convolutus, M. limatulus, and M. decipiens. 

 Collections.— (jceoXo^icdl Survey of England and Wales, Fearnsides. 



Group VII. 



Monograpti in which the mature thecte are more or less linear and isolate, with 

 reflexed terminations. 



In the Monugrapti included in this group the tendency to isolation reaches its 

 maximum development. The isolate linear appearance of the thecse foreshadowed 

 in the proximal portion of some of the species belonging to Group VI has now 

 become the predominating feature, and is characteristic, while the " adnate " 

 portion of the theca hardly deserves name as such, being sometimes so insignificant 

 that the whole " common body " of the polypary is reduced to a mere thread of 

 extreme tenuity. For the sake of convenience, therefore, we have taken the 

 length of the upper instead of the lower wall, as the conventional length of 

 the theca in this group. 



The form of the thecee was distinctly tubular, but whether it was cylindrical or 

 sub-rectangular there is not sufficient evidence to show ; some examples of Monog. 

 (B.) Linnsei and M. (R.) maxivius, however, suggest the latter shape. The length 

 of the thecse varies considerably, as does also their remoteness or nearness. The 

 mature thecae may vary in length from 1*5 mm. (If. [i?,] liijhvidas) to 1"8 cm. 

 (If. [S.] maximus). The fraction involved in the formation of the apertural barb 

 also varies very much — from a conspicuous fraction of about one-fifth (M. [R.j 

 ]u/bridas) to the merest tendency to reflexion — and this reflexion is often indeed 

 concealed from the observer, appearing either as a mere rounding off of the theca 

 at its extremity (ilf. [Ii.~\ peregrlnus) or as an abrupt truncation {M. [A'.] equl- 

 distans). 



The following species are included in this group : Monograpfus {Rastrites) 

 peregrinus, M. (R.) longispinus, M. (B.) setiger, M. (B.) hyhridus, M. (B.) approxi- 

 matus var. Geinitzi, M. (B.) fngax, M. [R.) Linnsei, M. {R.) maximus, M. (R.) 

 eqiiidistans. 



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