A typical graptolite consists of an axis bearing a series of tooth-like projections, like a saw.
The Silurian has in Sweden almost the same character as the Wenlock and Ludlow formation of England and consists partly of graptolite shales, partly of limestones and sandstones.
It is the general practice of palaeontologists to regard each graptolite polypary (rhabdosome) developed from a single sicula as an individual of the highest order.
Many Graptolite zones, showing a constant uniformity of succession, paralleled in this respect only by the longer known Ammonite zones of the Jurassic, have been distinguished in Britain and northern Europe, each marked by a characteristic species.
Graptolite Island now has a giant rookery - mainly Adelie Penguins.