30 TERMS USED 



Thirdly, of the Margin. 



That part of the margin which is opposite the beaks 

 (p/. 3. /. 26. Z>) is often called the upper margin, or margo 

 superior ; and, as the cartilage is considered by Linnsus as 

 occupying the anterior parts of the shell, so that part of the 

 margin which lies between the beaks and the end, on the side 

 where the cartilage is found (p/. 3. /. 26. c), is called the 

 anterior margin, and that between the beaks and the otlier 

 end (p/. 3. /. 26. cZ) the posterior margin ; the hollow or 

 cleft that is occupied by the cartilage is called rima anterior. 

 The margin is said to be integerrhims when it is smooth 

 without any notch or wrinkle, and is opposed to dentatus, 

 serratus, &c., as Donax cuneata, Vemis Chione, &c. 

 Acutus is when the margin is smooth, but thin and sharp, as in 



Mactra stidtoriim. 

 Dentatus is when the margin has small wrinkles, called teeth, 



as in Donax denticulatus. 

 Serratus is when the margin is toothed like a saw, as in Cai'- 



dium serration. 

 Crenatus is when the margin is wrinkled or notched, with 



larger wrinkles than dentatus, as in Area Glycymeris. 

 Plicatus is when the wrinkles are still larger, like plaits or 



folds, as in Area Pectuncidus and senilis. 



OF UNIVALVE SHELLS. 



The IT nival ve spiral shells are said to be involute or con- 

 volute. 



