Without a regular spire: 5 genera. [Sidenote: PATELLA. DENTALIUM. SERPULA.] "You are well acquainted with _Patella_, the limpet: one species of this genus is very common on the rocks by the sea-side. (Plate 1.) In the _Patella_ genus we lose sight of a spire; the shell is nearly conic, and shaped like a basin. The species are very numerous, exhibiting great variety of form; the number is two hundred and forty. "The form of _Dentalium_ is easily known. The shell is univalve, nearly straight, tubular, not chambered, and open at both ends. "The species called elephant's-tooth is slightly curved, the colour green, (Plate 2.) It is found in the European and Indian seas. There are only twenty-two species. _Dentalium entails_, the dog's-tooth, is very common. "The _Serpula_ genus is remarkable. The shells are tubular, frequently closed at one end. They are often found in clusters, adhering to rocks, stones, fuci, shells, &c. "There is _Serpula triquetra_ upon a _pecten_, (Plate 8.) [Sidenote: TEREDO. SABELLA.] "From the appearance of this piece of timber you may form some idea of the devastation committed by the _Teredo_, or ship-worm. (Plate 8.) The shell is tubular and flexuose; two valves at each end, and penetrating through wood. There are four species. [Illustration: Plate 8.] "_Sabella_ is the last genus, and a very remarkable one. The species are twenty-five, several of which are British, (Plate 8.) "Shell tubular, formed of sandy and calcareous particles, agglutinated, and inserted in a membranous sheath. _Sabella Belgica_ is found in Britain. _S. chrysodon_ is found buried in sea-sand, often several inches long; it is covered with fragments of shells, and so brittle that it is not easy to obtain a complete specimen. "We have now finished our Linnæan genera, and here we must pause for the present. If you wish for any assistance in your study of the thirty-six examples that I have given you, I shall be ready to afford you both any help that lies in my limited power." CHAPTER VI. [Sidenote: SYSTEM OF LAMARCK.] "Lucy and I have been collecting a variety of species," said Charles to his father, "since our last lesson in conchology. We have also seen several large collections of shells, one of which was arranged according to Lamarck. I was much pleased with the new genera taken from _Buccinum_, _Bulla_, _Turbo_, and others. "We are desirous of gaining information on this new system, if you can spare a little time to attend to us." "Willingly," replied Mr. Elliot; "I anticipated such a request, and have been making lists of the genera belonging to each system; so that, upon meeting with a new genus, you may be able to ascertain with some accuracy its place in the old arrangement.