32 



v/ill be easily understood. i Tor X/l'.- 



ti-ya in x'l/rc. 8-10. Fi . 



>s long as it is taken J'rom its tube, from the 

 loft . At tlie anterior end, on the left, th^ "head" 

 is covered by the small shell, over whose dorsal and poste- 

 rior portions iluplicatures of the mantle project. Behind 

 the shell, - long, naked body extends, tapering so that 

 the whole '".Vorm" forms a truncated cone. At the posterior- 

 end are si'.ovm the points of attachment to the calcareous 

 tube; and from it project the pallottes and siphons. From 

 the anterior end, between the gaping shell valves, pro- 

 jects the pestle-shaped foot. 



The nalced, projecting part of the body is tlie man- 

 tle. If it is removed (:'i:. 0) the long gills are ox - 

 posed posteriorly and the large visceral mass anteriorly. 

 The latter is continuous witli the foot and extends about 

 tv/o-fifths of the length of th.e body. It contains the 

 viscera (alimentary canal, genital organs, etc.). Dorsal 

 to it (fir;. 10) lies the large pericardial cavity v.-ith its 

 contained and associated sti'uctures (heart, kidneys, vis- 

 ceral ganglion). Dorsal to the pericardial cavity is the 

 long, narrow anal canal, into which the rectum opens above 



