MOLLUSC A, 115 



inhabitant been satisfactorily enlarged. The Dentalium im- 

 perforatum, trachea, and glabrum of Montagu's Testacca 

 Britannica, do not accord with the essential character of 

 the Linncean genus in being "utraque extremitate pervia." 



33. SERPULA. This genus has undergone several changes 

 in the hands of modern conchologists. The S. seminulum 

 has been transferred to the genus miliola, and the S.filo- 

 granum to the tubipora. Besides these trivial alterations, 

 the character has been greatly circumscribed, so as only to 

 include shells which adhere to other bodies, and are tubu- 

 lar, entire and flexuous, with a simple mouth, as represent- 

 ed by the S. contortuplicata of Linnaeus. The species 

 which are regularly spiral, discoid, and fixed, as the S. spi- 

 rorbis, now constitute the genus SPIRORBIS. But as there 

 are both dextral and sinistral shells with this character, 

 the dextral species may form the genus Spirorbis, while 

 the HETERODISCA may receive the reversed species. 



The genus VERMICULARIA is formed from those species 

 which, in appearance, resemble the spirorbis, but are not 

 adherent, such as the S. lumbricalis. The shell at the 

 mouth is, in general, somewhat produced. There are two 

 or three minute British shells of this genus. 



The genus SILIQUARIA, represented by the S. anguina, 

 is distinguished from the serpula by a longitudinal, lateral, 

 subarticulated fissure, which extends the whole length of 

 the shell. 



The genus PENICILLUS is formed from that curious shell 

 the S. penis, and well known by the name of the watering- 

 pot. The disk is perforated by a number of small holes. 



34. TEREDO. From this genus, now considered as a bi- 

 valve (the tube being regarded as an accessory covering), 

 the FISTULANA, of which T. clava of Gmelin is the 



