RETIOLITES. 



339 



lines of growth. Clathria very ill-defined. Reticula delicate and fibrous, 

 with sub-rectangular meshes. 

 Description. — The outline of the complete polypary is generally very badly 

 defined, the actual positions and courses of the ventral and apertural margins 



Figs. 221 a — c. — Gladiograptus perlatus (Nich.). 





! 



\ri ■ 





being only identifiable at intervals. 



The elements of the clathria are as a rule 

 almost indistinguishable, the straight septal 

 strand and a few of the parietal bars being the 

 only parts well shown. The reticula is very 

 delicate and fibrous, and its meshes are 

 usually sub-hexagonal. In some specimens 

 (PL XXXIV, figs. 10 b and d), especially in the 

 earlier portions of the polypary, the reticula 

 has apparently disappeared altogether, and 

 what appear to be the interthecal planes or 

 floors of the thecce are exposed, and these 

 form parallel bands separated from each other 

 by bare interspaces of about the same breadth. 

 These floors are membranous, and are some- 

 times crossed by a series of fine growth-lines. 

 This feature is very characteristic of most 

 examples of the species. 



Affinities. — G. perlatus somewhat resembles 

 G. Geinitzianus in its structure, but its different 

 shape, its much more delicate reticula and ill- 

 defined clathria are well-marked distinctions. 

 Horizon and Locality. — Llandovery, Birkhill Shales (zone of Monog. gregarius 



to zone of Monog. Sedgwichii), Skelgill Beds. 



Ireland : Coalpit Bay, Donaghadee, Co. Down. S. Scotland. : Dnffkinnell Burn, 



near Wamphray; Cramalt, Meggat Water; Dobb's Linn, etc. Lake District : 



Mosedale in Long Sleddale, Browgill. 



Associates, etc. — Gladiog. perlatus is a rare fossil in the Llandovery Beds, in 



which it occurs in the zone of Monog. gregarius associated with Monog. gregarius, 



Petalog. minor, Climacog. Toruquisti, CI. Hughesi, and other forms, and in the higher 



zone of Monog. Sedgwichii, with M. Sedgwichii, M. convolutus, M. lobiferus, M. 



discretus, Orthog. bellulus, and Climacog. scalaris. 



Collections. — Belfast Museum of Natural History, British Museum (Natural 



History), and Lap worth. 



a. Distal fragment, showing texture of reti- 

 cula. Enlargement of part of PL XXXIV, 

 fig. 10 c. 



h. Specimen showing the interthecal planes or 

 floors. Enlargement of part of PI. XXXI V, 

 fig. 10 6. 



c. Thecae showing the floors marked by growth- 

 lines ; also the zigzag septal strand. En- 

 largement of part of PL XXXIV, fig. 10 d. 



