50 



[Assembly 



canal, affixed by a slender radix or pedicle from the centre of the exterior 

 side. 



The fragments, either simple or variously branched, hitherto described 

 as species of Graptolithus, are for the most part to be regarded as detached 

 portions from the entire frond. 



In the living state, we may suppose those with the corneous disks and 

 numerously branched fronds to have been concavo-convex (the upper being 

 the concave side), or to have had the power to assume this form at will. In 

 many specimens there is no evidence of a radix or point of attachment, and 

 they have very much the appearance of bodies which may have floated free 

 in the ocean. 



The accompanying figure 1 is the central portion of one of these grapto- 

 lites, showing the bilateral arrangement of these branches and the bifurcation 

 of the same. The disc enclosing the bai.es of the branches is well preserved, 

 while most of the rays are broken off a little beyond its margin. The side 

 presented is the lower or exterior of the specimen, and the serratures are 

 not visible. 



Fig. 2 is a specimen of the same species, from which the substance of the 

 disc is removed, showing the serrated margin which is compressed in that 

 direction. 



Illustrations of Graptolithus losani. 



