Graptolites , (Gr. to write, and stone), a genus of fossil acalephs, of as many as 20 species, found only in the Silurian rocks, abounding particularly in the slates of the Hudson river group. So numerous are these early forms of zoophytes in the Llandeilo rocks of Europe, that it has even been thought probable that the carbonaceous character of the slates was owing to the abundance of their remains. As found in the black slates, their silvery forms arc obscurely retained, and the fossils may easily be mistaken for impressions of plants. They arc long and slender, resembling some alga), as well as the feather part of a quill, whence their name. When found in calcareous strata their forms are more distinct. Their nearest living analogues are the sea firs or sertularians, of which the species inhabit muddy sediment, such as the black slates must once have been.

1. Graptolithus Logani, showing the centre of a branching group. '2. Portion of a branehlet. 3. Same much enlarged. 4,5. Forms of Phyllograptus typus. 6. Graptolithus pristis. 7. Young of a graptolite.