Species in which the circumference of the disk is without a fringe.
2. Clavagella. One species.
An irregular tube, with branches or projecting tubes at the closed end; within it is one free or moveable valve, united by a ligament to another, which is blended with the tube; this distinguishes it from the Aspergillum. Found in sand and coral.
Shell oval, very slightly elongated, striated longitudinally, slightly irregular; equivalve, inequilateral; hinge a little variable; ligament exterior; two well-marked distant muscular impressions; a calcareous sub-cylindrical tube, more or less completely surrounding the shell, and terminated before by a single orifice.
C. aperta. The open Clavagella.
Tube erect, adhering; aperture waved, entire, expanding, funnel-shaped, leaving the two valves open or uncovered in all their anterior part; with an ovate face valve.
3. Fistulana. Four species.
Lamarck asserts that the tube and shell of this genus are quite distinct. It so greatly resembles the Teredo that it is with difficulty distinguished. It is found in sand, wood, stone, and sometimes shells.
Shell annular or very short, not sharp nor angular anteriorly, but in other respects much like that of the Teredo.
Tube generally shorter, thicker, more solid, more club-shaped than that of the Teredo, always closed at its anterior extremity in such a manner as to contain and entirely hide the shell; the posterior extremity open, and divided interiorly into two syphons by a partition.