UNIVALVES. DENTALIUM. 143 



Other species are smooth, or covered with striae, so mi- 

 nute that they cannot be discovered without the aid of a 

 magnifying glass. Of these, the D. pellucidum is an ex- 

 ample ; it is of a horny or pale honey colour, very narrow 

 and thin, and does not effervesce in acids ; it is an inhab- 

 itant of the Northern seas, and about two inches and a 

 quarter long. The D. entalis, which is an inhabitant of 

 the Indian and European shores, is generally an inch and 

 a half long, and of a reddish or pale yellow colour, and 

 the tip is often tinted with orange or pink. 



The D. minutum inhabits the Mediterranean ; it is a 

 round, straightish, smooth shell, and so very minute as 

 scarcely to be discernible by the naked eye ; it resembles 

 a small bristle, or one of the spines of an echinus. 



The D. imperforatum (from Sandwich and its neighbour- 

 hood) is also a minute species, and is by no means com- 

 mon. 



The recent species are mostly from the Indian and Eu- 

 ropean oceans j though some few are from the Mediterra- 

 nean and Northern seas, and one species inhabits the shores 

 of Africa. 



DENTALIUM Tooth- SMI. 



FAMILY I. With longitudinal ribs. 

 Rectum Straight. *Striatum Striated. 



Elephantinum Elephant's. *Dentalis Curved- striated. 



Aprinum White-ribbed. Fasciatum Banded. 



* Imperforatum Minute-truncated. 



FAMILY 2. With annular strife. 



Politum Ring-striated. Eburneum Smooth-ivory. 



*Trachea Minute-windpipe. 



FAMILY 3. Smooth. 



*Entalis Common. *Gadus Hake's. 



Corneum Horn-colour' d. *Minutum Minute. 



Pellucidum Pe Ihicid. 



