76 GLOSSARY. 



Crenated. Applied to small notches not sufficiently defined 



to be called teeth. 

 Decussate. Intersected by striss crossing each other. 

 Denticulated. Having little teeth or raised points. 

 Decctral. Place the point of a spiral shell towards the eye 



with the moath downwards ; if the aperture be on the 



right side of the axis, it is a dextral shell, if otherwise, 



it is sinistral or reversed. 

 Discoidal. When the whorls form a flattened spire. 

 Dorsal. A dorsal shell is one placed upon the back of the 



animal. The dorsal margin of a bivalve shell is that 



on which the hinge is placed ; the opposite is called 



ventral. 

 Epidermis. The fibrous, horny, external coating of shells. 



The outer covering of extraneous matter with which 



some shells are generally coated. 

 Epipliragm. The membranous or calcareous substance 



with which some moUusks close the aperture, when 



they retire to hibernate, 

 Equivalve. A term applied to a bivalve shell when the 



valves are equal to each other in dimensions. 

 JExternal. A shell which contains the animal, and is not 



covered by the mantle. 

 Granulated. Covered with minute rough grains. 

 Hinge. The edge of the bivalve shells near the umbones, 



including the teeth and ligament. 

 Inequilateral. A term applied to a bivalve shell when its 



extent on one side of the umbones is greater than that 



on the other. 

 Inequivalve. The two principal valves differing from each 



other in diameter or convexity. 

 Inflected or Inflexed. Turned inwards. Applied to the lip 



of a spiral shell when turned towards the body whorl. 

 Inner lip. That edge of the aperture of a univalve shell, 



which is near to the imaginary axis, as distinguished 



from the outer lip, or that which is on the outer side. 

 Internal ligament. The ligament of a bivalve shell which is 



placed within the closed part of the hinge, so as not to 



be seen when the valve is shut. 

 Keel. A flattened ridge, resembling the keel of a ship. 

 Lamellated. Having the layers of which the shell is com- 

 posed overlaying each other. 



