SUPPLEMENT. 501 



GEXUS GRAPTOLITIIIS ( LiNN^us). 



CoRALLtJM or bryozoum fixed ( free ? ), simple or compound ; the parts bi- 

 laterally arranged, consisting of simple stipes or of few or many simple 

 or variously bifurcating branches, radiating more or less regularly from 

 a centre, and, in the compound forms, united towards their base in a 

 continuous thin corneous membrane or disk formed by an expansion of 

 the substance of the branches, and which in the living state may have 

 been in some degree gelatinous. Branches with a single or double series 

 of cellules or serratures, communicating with a common longitudinal 

 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 Graptolitbus, 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 ap- 

 pearance of bodies winch may have floated free in the ocean. 



The accompanying figure 1 is the central portion of one of these graptolites, 

 showing the bilateral arrangement of these branches and the bifurcation of the same. 

 The disc enclosing the bases of the branches is well preserved, while most of the 

 rays are broken oflf 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. 



Fig. 3 shows the central portion or radix, with the bases of the branches; while 

 two of these are shown in their extension, laterally compressed and showing the 

 serratures. The entire length of some of these branches is about seven inches. 



