372 INTRODrCTIOK TO CONCHOLOGY. 



nearly equilateral, always remaining open, and supposed to 

 cover a portion of the animal's back ; in this position it be- 

 comes imbedded at the lower side of a long clavate testa- 

 ceous tube, so that the umboes and complete form may be 

 distinctly traced on the outer surface : the tube is then 

 elegantly closed over by a convex disc, perforated with nu- 

 merous tubular holes, like the rose of a common watering- 

 pot. A small fissure is obvious in the centre, and the 

 margin is surrounded by a conical frill or row of tubes, 

 supposed to be filled with fleshy filaments from the 

 mantle, in living specimens. The upper end of the tube, 

 which is rarely perfect, is more or less attenuated, and, 

 gracefully terminating in smooth undulations, is reflected at 

 the margin ; occasionally, however, the tube is straight, and 

 slightly compressed. The reflected extremity is left entire 

 at certain periods of grow^th, and the tube is recommenced 

 according to the exigencies of the animal ; some specimens 

 have been discovered with four or five entire terminal re- 

 flections. 



Observe the curious construction of the Clavagella, and 

 the admirable appendage with which he is endowed. This 

 creature is also found buried in stone, with the clavate or 

 chambered end downward. The tube has a kind of per- 



