34 



external fixed valve, the other free and internal; and 

 from the latter, which has no perforations at the larger 

 extremity. This shell has also an appearance of small 

 projecting tubes at one extremity round the disk, simi- 

 lar to those of the Aspergillum. Sowerby in his Ge- 

 nera of Shells, No. 13, has described the only recent 

 species of this genus supposed to be known, under the 

 name of 



Clavagella aperta. 



J. 



** 



FISTULANA. W 



Encycl. Method, pi. 167, fig. 1 7, 22. 

 La Marck asserts a singular fact with respect to this 

 genus. He, like all other naturalists, had considered 

 these tubes, as well as those of the Aspergillum and 

 Clavagella, which inclose the animal, to be the shells 

 themselves; but has now ascertained them to be quite 

 distinct. The Fistulanae have their shell free and de- 

 tached, within the sheath, and neither of the valves 

 fixed into the partition of the tube, which is most ge- 

 nerally testaceous, closed, and retort-shaped at the pos- 

 terior extremity, attenuated to the other end, where 

 it is open, containing a bivalve shell, the valves of 

 which are equal, but gaping. 



