_F. gregata._ The gregarious Fistulana. Sheath or tube doubly club-shaped, congregating; shell angularly arcuated, with double angulated serrated wings. _F. Clava._ The Club Fistulana. Pl. 33, fig. 5. Species with one end clavate, the other incurved, narrower, obtuse, and perforated in the middle; shell generally flexuous, of a brownish colour; exterior rough, interior smooth. 4. Septaria. One species. The tube of this genus unquestionably contains a bivalve shell; but, as no perfect specimen has yet been found, nothing decisive is known respecting it. Tube calcareous, thick, conically elongated, more or less flexuous, as if composed of pieces placed on the ends of each other, or as if articulated, with a ring or projection more or less marked at the place of the joints, but without traces of partitions; terminated on one side by an inflation, oftentimes with some interior partitions, and on the other by two tubes, distinct and sub-articulated. _S. arenaria._ The Sand Septaria. The type of this genus. 5. Teredina. Two fossil species. A genus without a living species, given here to preserve the family entire, having a shell thick, oval, short, very gaping posteriorly, equivalve, inequilateral; summits well marked; a spoonlike cavity in each valve. Tube or sheath testaceous, cylindrical; anterior end open; posterior end closed, but exhibiting the two valves of the shell. 6. Teredo. The Ship Worm. Three species. This genus derived its name from the faculty it possesses of boring wood. The T. navalis can penetrate the stoutest oaken planks of a ship’s sides by means of two valves affixed to the head of the animal. The effects produced would be much more destructive but from the fact of their generally perforating the wood in the direction of the grain. Sir E. Home wrote a very scientific and interesting description of a species not mentioned by Lamarck, called the T. gigantea, found imbedded in indurated mud in the Island of Sumatra. It is the largest species known, some having been seen four or five feet long. Shell thick, solid, very short or annular, open at both extremities; equivalve, equilateral, angular and sharp anteriorly, only slightly touching by the opposite edges; hinge obsolete; a considerable internal spoonlike cavity; one slightly sensible muscular impression. Tube more or less distinct from the substance in which the animal lives, cylindrical, straight or flexuous, closed with age at the oral extremity so as to envelop the animal and its shell; always open at the other end, and divided interiorly into two syphons by a middle partition. Teredo navalis. T. palmulata. T. gigantea. _T. navalis._ The common Ship Worm. Species very thin, cylindrical, and smooth; slightly twisted, white, finely striated longitudinally.