[2] The number of the British fossil species of the Balanidæ and Verrucidæ in a recognisable state is so small, that I do not know whether it will be considered worth while to publish in the Palæontographical series more detailed illustrations than are given in this volume. In nomenclature, I have endeavoured rigorously to follow the rules of the British Association, and have never, at least intentionally, broken through the great law of priority. In accordance with the rules, I have rejected, that is, as compulsory, all names given before the introduction of the binomial system in 1758. I have given much fewer synonyms than is usual in conchological works; for it is impossible to recognise with any approach to certainty, several even of the common European forms, in the short descriptions given by most authors; this holds good in many cases in which figures, in appearance excellent, have been added. I assert this the more confidently, from having had the advantage of having gone over some of the Linnean synonyms with Mr. S. Hanley. I may further venture to express my conviction, that giving references to works, in which there is not any original matter, or in which the plates are not of a high order of excellence, is absolutely injurious to the progress of natural history. NOMENCLATURE OF THE SHELL OF A SESSILE CIRRIPEDE. [Illustration: SHELL. Fig. 1. _Orifice_ of shell, surrounded by the _sheath_. _Sheath_ formed by the _alæ_ (_a_--_a_.) and by portions of the upper and inner surfaces of the _parietes_ (_p_--_p_.) N.B. In Balanus, and many other genera, the Rostrum and Rostro-lateral compartments are confluent, and hence the Rostrum has the structure of Fig. 2.] COMPARTMENTS. [Illustration: Fig. 2. Fig. 2. Compartment with two radii, serving either as a Rostrum or Rostro-lateral compartment.] [Illustration: Fig. 3. Fig. 3. serves as a Lateral and Carino-lateral Compartment.] [Illustration: Fig. 4. Fig. 4. serves as a Carina or Rostrum.] OPERCULAR VALVES. [Illustration: Fig. 5. SCUTUM (internal view of).] [Illustration: Fig. 6. TERGUM (external view).] [Illustration: Fig. 7. TERGUM (internal view).]