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BRITISH QRAPTOLITES. 



Pig. 217 a — c. — Nymphograptus velatus, sp. nov. 





'A 



1 



v 





* 



& 



: 





curved ventral meshes apparently corresponding to the ventral meshwork in 



Thysanogra/ptus, and a second set 

 of straight and sub - parallel 

 strands united with each other 

 and to the first set by cross 

 threads at fairly regular intervals. 

 The main filaments belonging 

 to the first set have the appear- 

 ance of prolonging the apex of 

 the apertural denticle, as in ILillo- 

 gra/ptus. Interiorly they are 

 each distinctly carried backwards 

 continuously until they unite with 

 one of the septal strands of the 

 clathria. Exteriorly they curve 

 gracefully downwards and are 

 connected with the correspond- 

 ing filaments proceeding from 

 the thecas immediately below, 

 as in Thysanogra/ptus ; there 

 appears also to be a secondary 

 reticulation on the outer side 

 of the descending fibres as in 

 that sub-genus. 



The main filaments belonging 

 to the second set appear some- 

 what stouter. They are straight 

 and as a rule parallel, and have an outward and ascending direction answering 

 more or less to the inclination of the ventral walls of the thecaa. They are of 

 great length, some of them being prolonged to a distance corresponding to the 

 extent of from 10 to 12 theca3, and they are united by more delicate cross-threads, 

 usually somewhat curved and set at distances approximately equal to the distance 

 which separates the apertures of the thecse. 



Whether the straight strands of the external lattice-work originate directly 

 from the septal strands of the clathria in the manner of the septal processes and 

 scopulas of Hallograptus and Neurography (see postea) is not certain ; but in any 

 case both the curved and the straight sets of filaments are united into a common 

 extraneous lacinia, which apparently surrounds the whole polypary. 



It is probable that the parallelism of the long straight strands is not original, 

 but due in part to the direction in which compression has been effected, for some 

 of those in the proximal region certainly widen the distance between them as they 



a. Sub-scalariform view, showing form of fchecse. Enlargement of 



part of PI. XXXIV, fig-. 4 b. 



b. Scalariform view, showing part of lacinia. Enlargement of 



part of PI. XXXIV, fig. 4 a (left-hand specimen). 



c. Ibid., showing lacinia in its most complete form. Enlargement 



of part of PI. XXXI V, fig. 4 a (right-hand side specimen). 



