LmeiT Silurian.] PALEONTOLOGY OF VICTORIA. IGraptolites. 



slender non-celluliferous base ; and I think the term might be advan- 

 tageously extended to the more complex species, not then knoAvn, in 

 which four, eight, or a greater number of precisely similar stems 

 are similarly united at the base. The number of the branches could 

 not possibly be accepted as a generic character on any analogy 

 with the living Hydrozoa, such as Se7-tularia, Plumularia, &c., 

 which are the nearest known allies of the Graptolites ; and yet the 

 genera Tetragraptus., Loganograptus, &c., have been mainly pro- 

 posed on this ground, and I do not therefore adopt them — the 

 portions of the stems, if found singly, being undistinguishable. In 

 some individuals of some of these other species a horny disc has 

 been observed connecting the bases of the stems, but it is more 

 often absent, and its nature is not known. 



The following descriptions and figures on our second plate 

 illustrate four of those very compound species so exceedingly rare 

 in Europe and the United States, but abounding, as shown by 

 Professor Hall, in Canada, and, as I find, just as common in 

 Victoria. 



In the above-mentioned work I proposed the separation of the 

 simple stems with the two rows of cells as a distinct genus under 

 the name Diplograpsus, universally adopted since by Palaeon- 

 tologists. And, as these are confined to rocks of the Lower 

 Silurian or Cambrian age, while those with a single row of cells 

 are common to those rocks and the Upper Silurian, the generic 

 discrimination of these two types of structure is of great im- 

 portance to the geologist, who has thus a means put in his hands 

 of recognising the older age of any formation in which he might 

 find the smallest fragment of one of these double-celled Graptolites. 



I have adopted here Professor Hall's view of the generic 

 separation of those leaf-shaped forms, apparently composed of four 

 semi-elliptical parts, joined at right angles by the straight back of 

 the common canal at the base of each row of the cells. These 

 forming the genus Ph/Uograpltis are also confined to the Lower 

 Silurian or Cambrian rocks. 



[fi ] 



