RETIOLITES. 



337 



Figs. 220 a, b, and c. — Gladiograptus Geinitzianus (Barr.). 



a. Distal fragment, showing straight and zigzag septal strands. 



Enlargement of part of specimen from Listice, Bohemia ; Etage 

 Ee. Coll. Sedgwick Museum. 



b. Distal thecse, obverse aspect, showing apertural denticles ; also 



texture of reticula. Enlargement of part of PI. XXXIV, fig. 8 b. 



c. Sub-scalariform view, showing ventral lattice and parietal ledges. 



Enlargement of part of specimen from Kepora, Bohemia. Coll. 

 Lapworth. 



appearance according to the amount and direction of compression ; in some cases 

 the ventral edge has the appearance of being straight and continuous, in others 

 the compressed thecal apertures appear concave and strongly mucronate. 



The substance of the reticula 

 is thick compared with that of 

 other British species in this 

 family, and the tracery only 

 occasionally appears to be 

 actually fibrous or filamentous. 

 Its interspaces are irregular in 

 form and vary in number from 

 three to four within the space 

 limited by the distance be- 

 tAveen the floors of successive 

 thecae. 



The clathria is often well shown in British examples of this species, but 

 as few of them are preserved even in semi-relief the details are difficult of inter- 

 pretation. Fortunately the elements of the entire clathria and their relations have 

 been admirably worked out for European examples by Holm, Tornquist, and 

 others, and reference may be made to their illustrative figures and descriptions 

 and also to the terminology already summarised on pp. 305, 306. 



The reticula covers all the panels formed by the outer walls of the thecse, and 



is attached to the parietal 



lists, into which its threads 



appear to graduate. It also 



extends over the surface of the 



central parts of the polypary 



beyond the outwardly visible 



limits of the parietal lists, so 



that both in the obverse and 



reverse aspect of the polypary, 



when preserved in full or in 



half relief, there is a central 



longitudinal field destitute of 



other structure, and the septal 



strands and aboral lists are 



invisible (Fig. 220 e). 



Affinities, etc. — Gladiog. Geinitzianus does not appear to have any close allies in 



Britain with the exception of var. angustidens. It is distinguished from all 



other species by the form of the polypary and the characters of the clathria and 



reticula. 



44 



Pigs. 220 d, e, and/. — Gladiograptus Geinitzianus (Barr.). 



d 



f 



d. Restoration of proximal portion, showing clathria and parts of 



reticula. (After Halm.) 



e. Transverse section, showing relations of clathria and reticula. 



(After Holm.) 



f. Diagram of clathria only. Strands : s. Straight septal strand ; 



z- zigzag septal strand ; v. ventral strands. Lists : a. Apertural 

 or oral; i. interior or aboral; p. parietal. Those elements 

 marked (1) belong to the obverse aspect; those marked (2) to 

 the reverse aspect. 



