Transactions. 81 
sea bottom, where those serriated and curiously-formed Zoophytes, 
named Graptolites, seemed to have swarmed in extraordinary 
abundance ; and, as far as we at present know, they began life 
in the Silurian system, lived throughout the whole period, and 
died out at the close of that formation. Although their geologi- 
cal range is not extensive, being confined to these old Silurian 
rocks, their geographical range is very expansive, being found in 
the British Isles, Australia, States of America, Canada, and 
various parts of the continent of Europe. It seems a difficult 
matter to determine to what class the Graptolitide belong, some 
authorities believing that they are nearly related to the Virgu- 
laria of the present seas, others to the Polyzoa, and others to 
Sertularia or Hydrozoa, because they have a chitinous or horny 
exterior, with hydrotheca or cells; but the Sertularia have no 
solid axis, neither are the cells overlapping each other like those 
of the Graptolitide. Again, the Polyzoa possess a calcareous 
exterior, and in that case are dissimilar. It was thought at one 
time that Graptolites attached themselves to the rocks or other 
objects at the sea bottom, while some observers say they were 
free-floating. From a number of specimens obtained about two 
years ago, I am thoroughly convinced that the greatest number 
were fixed bodies, especially the genus Monograptus. In the 
genera Diplograptus and Didimograptus, there are numbers of 
species which have no radical point of attachment, so I think we 
may conclude that they were both fixed and free-floating. On 
the other hand, the Polyzoa, with one exception, Christatella, a 
fresh water species, are all attached to some object, and also the 
whole of the Sertularia. General Portlock appears to have been 
the first to suggest definitely that the Graptolites were allied to 
the Sertulariz and Plumulariz ; however, all modern observers 
are now agreed in placing the Graptolites somewhere among the 
Hydrozoa. 
I think it may be advisable just now, as there may be some of 
the members present who are unacquainted with the Grapto- 
litide, to explain the structure of these interesting Zoophytes, 
and with which I will be as brief as possible. Unfortunately, 
they are rather small objects, but with the aid of these large 
drawings, and also this model of a Graptolite, I hope to make 
the description of them much plainer than by describing the 
specimens you see on the table. When we describe one we 
describe the whole of the genus Monograptus, the polypery being 
1 
