416 



THE OPISTHOBRANCHIATE 



Postscript. — The word " height " in reference to the central teeth 

 is used in these Tables to denote what is in reality their " length.'' 

 The " height " of the basilar portion is its antero-posterior dimen- 

 sion in the middle line, i.e. the length of the line joining the median 

 points of the anterior and posterior bays. The " heighf of the 

 cusped ridge is the length of the same line terminating posteriorly 

 at the apex of the central cusp. The breadth of the basilar portion 

 is its maximum breadth posteriorly. 



Such a formula as tI'I'tI was suggested to me by Mr. Weldon, 

 to indicate the number of lateral teeth in an anterior and posterior 

 row of the radula at the same time. This formula denotes an 



