In writing the name of a species, it is important to append the name, often in an abbreviated form, of the author who first proposed the accepted specific designation. _Stigmaria ficoides_ Brongn. written in this form records the fact that Brongniart was the author of the specific name _ficoides_. It means, moreover, that Brongniart not only suggested the name, but that he was the first to give either a figure or a diagnosis of this particular fossil. It is frequently the case that a specific name is proposed for a new species, without either figures or description; such a name is usually regarded as a _nomen nudum_, and must yield priority to the name which was first accompanied by some description or illustration sufficiently accurate to afford a means of recognition. A practice which may be recommended on the score of convenience is to write the name of the author of a species in brackets if he was not the first to use the generic as well as the specific name. _Onychiopsis Mantelli_ (Brongn.) tells us that Brongniart founded the species, but made use of some other generic name than that which is now accepted. This leads us to another point of some importance. Brongniart described this characteristic Wealden fern under the name _Sphenopteris Mantelli_; _Sphenopteris_ being one of those extremely useful provisional generic terms which are used in cases where we have no satisfactory proof of precise botanical affinity. _Sphenopteris_ stands for fern fronds having a certain habit, form of segment and venation, and in this wide sense it necessarily includes representatives of various divisions and genera of Filices. If an example of a sphenopteroid frond is discovered with sori or spores sufficiently well preserved to enable us to determine its botanical position within narrower limits, we may with advantage employ another genus in place of the purely artificial form-genus which was originally chosen as a consequence of imperfect knowledge. Fronds of this Wealden fern have recently been found with well defined fertile segments having a form apparently identical with that which characterises the polypodiaceous genus _Onychium_. For this reason the name _Onychiopsis_ has been adopted. It is safer and more convenient to use a name which differs in its termination from that of the recent plant with which we believe the fossil to be closely related. A common custom is to slightly alter the recent name by adding the termination _-opsis_ or _-ites_. There are several other provisional generic terms that are often used in Fossil Botany, and which might be advantageously chosen in many cases where the misleading resemblance of external form has often given rise to the use of a name implying affinities which cannot be satisfactorily demonstrated.