322 PLAXIPHORA. 



jugum of the intermediate valves (and anterior area of the posterior 

 valve). Under surface of all the valves of a bluish-green color ; 

 laminae of insertion paler. Girdle, upper surface dark brown ; 

 under surface dusky orange. 



Length 40, breadth 25, height 10 mill. ; angle of divergence 125 

 to 135 (two specimens from 100 to 150 fathoms.) 



Length 25 to 35, breadth 14 to 17, height 8 to 9 mill.; angle 90 

 to 110 (two shore specimens.) 



Group of P. wahlbergi. 



No sculpture except some concentric lines; sinus deep, dentic- 

 ulate ; girdle without sutural tufts. 



P. WAHLBERGI Krauss. PI. 55, figs. 17, 18. 



Shell ovate-oblong, slightly convex ; brown with a chestnut-brown 

 median band and two yellowish longitudinal bands. Concentrically 

 sulcate. Interior white, brownish-violet in the middle. Anterior 

 valve semilunar ; posterior valve subtriangular, depressed ; inter- 

 mediate valves subreniform, having distant concentric grooves on 

 the front part of the central areas, and on the lateral areas. Girdle 

 brown, leathery, velvety. Length 15, breadth 9 lines. 



This species has rather thick, little convex valves, rounded on 

 their outer ends, and having the older or posterior half of each 

 eroded, and deprived of color and sculpture. Lateral areas not 

 differentiated. The forward part and the sides of each valve have 

 6 or 7 separated, sometimes finely granulated furrows, parallel with 

 the margins. The posterior margin is eroded, probably beaked in 

 the middle. The insertion-plates are narrow, roughened outside. 

 Anterior valve excavated behind, having 8 slits. Posterior valve 

 lacking teeth. The valves have in the middle a chestnut-brown 

 shining band, 2 mill, wide, on each side of which a yellow streak of 

 greater or lesser width generally lies ; but usually they are eroded 

 and gray. (Krauss.) 



Table Say, Cape of Good Hope. 



Chiton ivahlbergi KRAUSS, Die Sudafrik. Moll., p. 36, t. 3, f. 1 

 (1848). Euplaciphora wahlbergi CPR., MS. 



May be known by the separated concentric grooves of lateral and 

 central areas, parallel with the valve-margins, and also by the sinus, 

 which is deep, narrow and denticulate, the last being an unusual 

 character in this genus. The girdle has irregular setse. 



