GLOSSOGRAPTUS. 307 



tation. Not only do these appearances alter with every change in the amount 

 or the direction of compression, but owing to the general tenuity of the test the 

 upper and lower faces of the fossil as presented, are often shown in superposition 

 in the same view. 



As regards the general mode of development of the initial part of the polypary in 

 the Glossograptidse, it resembles in the main that of the Diplograptidge. 



As respects the systematic 'position of the Glossograptidse, the general form of the 

 polypary and the shape of the thecas, both indicate a close relation to the 

 Diplograptidse, but the localisation of the thickening in the test resulting in 

 the ultimate development of the skeletal frame-work is indicative of a most 

 intimate relationship with the family of the Retiolitidse, with which it was originally 

 associated by Lapworth in 1873 (' Geol. Mag.,' vol. x, p. 555), to constitute the 

 section Retioloidea. 



AYithin the limits of the family of the Glossograptidas, as at present understood, 

 there are three divisions, typified respectively by the genera Glossograptus, Lasio- 

 grajytus, and Betiograptus (Clathrograptus) . 



In the genera Glossograptus and Betiograptus the thecas are of the type of 

 those of Ortliograptus : in the genus Lasiograptus they are usually of the type 

 of those of Amplevcograptns. 



Genus GLOSSOGRAPTUS, Emmons. 

 1855. Glossograptus, Emmons, American Geology, vol. i, p. 108. 



Polypary bilaterally symmetrical, truncate) - elliptical in transverse section, 

 provided with both apertural and septal processes. Apertural processes 

 simple paired spines ; septal processes in the form of stiff, blind spurs. 



Thecse of the general type of Orthograptus. 



Test membranous, continuous, attenuated. 



The truncato-elliptical transverse section of the polypary is evidenced by its 

 lesser breadth when seen in the scalariform view, as compared with its breadth in 

 the bi-profile view, and the still greater width when seen diagonally. 



In the general mode of development of the proximal end the Glossograpti 

 resemble the Diplograptidas ; the sicula and earlier thecae, however, are relatively 

 more spinose. The downward direction of the earlier spines, combined with the 

 more or less horizontal growth of th. I 1 and th. I 2 , give the proximal part of the 

 polypary an appearance recalling that of the Phyllograpti. 



In Glossograptus each theca has at least two apertural spines, though it not 

 infrequently happens that, owing to the direction in which compression has been 

 effected, only one is visible. These apertural spines may be stout or slender, but 



