4 GENERA OF SHELLS. 



MALDANIA. 



Tube open at both extremities. 



CLYMENE. Tube slender, open at both 

 ends, encrusted exteriorly with grains of sand 

 and fragments of shells. 



C. amphistoma. 



DENTALIUM. Tube testaceous, nearly regu- 

 lar, slightly curved, gradually tapering towards 

 the posterior extremity, and open at both ends. 



(a.) Tube with longitudinal ribs or striae. 

 D. elephantinum, aprinum, sulcatum, fasciatum, octo- 

 gonum, cleforme, novemcostatum, scxangulare, striatum, 

 dentalis, pseudo-antalis, radicula. 



(b.) Tube without ribs or strice. 



D. antalis, arietinum, corneum, nigrum, politum, ebur- 

 neum, clava, fissura, coarctatum. 



AMPHITRITEA. 



Tube membranous or corneous ; more or less sandy. 



PECTINARIA. Tube an inverted cone, mem- 

 branaceous or paper-like, sandy, not attached. 



P. belgica, capensis, 



SABELLARIA. Tubes numerous, united in a 

 common honeycomb mass above ; composed 

 of agglutinated grains of sand and fragments 

 of shells ; orifices cup-shaped. 



S. alveolata, crassissima. 



TEREBELLA. Tube elongated, cylindrical, 

 attenuated and pointed at base, membranous, 



