BEDXALL : SOUTH AUSTRALIAN POLYPLACOrnOEA. 



149 



were at Dr. Carpenter's command, and those exceedingly small, I may- 

 be permitted to write more fully in regard to the coloration, having 

 numerous examples to work from. The ground tint is grey, speckled 

 with minute sky-blue, or emerald-green spots, sometimes intenningled 

 with angular blotches of white, the spots and blotches often surrounded 

 by a setting of golden brown, giving the surface a beautiful opalescent 

 hue. On the summits of the valves the coloration is distinct and 

 decided : in the majority of specimens the anterior valve is painted 

 with a white blotch, the second, third, and fourth with black blotches, 

 the fifth and sixth with broad white blotches, that on the sixth always 

 the larger, in fact the largest of all of them, giving place on the 

 seventh to a narrow white line, while on the posterior valve the white 

 blotch increases in size again, and forks from the umbo into two 

 divergent white streaks to the margin. The only variation from this 

 style of painting is when the black blotches of the second, third, and 

 fourth valves give place to white, in which case there is an irregular 

 line of white on the summit from one end of the shell to the other. 

 The girdle is white, painted at varying distances with naiTow black 

 stripes. /. virgatus should not be confounded with /. leniiginostis, 

 which differs from it both in shape and markings and in the nature 

 of the girdle-scales. 



17. IscHNOCHiTON Thomasi, u.sp. PI. XII, Figs. 4 and 5. 



This name is proposed for an Ischnochiton belonging to the group of 

 I. smaragdinus, I. lentiginoses, I. Mayi, and I. virg at us, but most nearly 

 allied to the first of these. The general contour 

 is that of /. smaragdinus, or somewhat narrower ; 

 and the tail valve differs in having the slope 

 behind the mucro notably concave, while in 

 /. smarngditius it is nearly straight. The 

 colour-pattern is unlike any of the varieties of 

 Angas' species, being closely mottled in rather 

 chequered design with white, blue, and light- 

 orange, mingled in varying proportions on 

 different specimens ; and there are usually olive 

 clouds on each side of the ridge, accompanied 

 by whitish streaks or spots, and on the tail 

 valve these marks often diverge backward. 

 Along each sutural margin there are two to 

 four dark dots on each side. The general tone 

 is a light greenish-yellow. Girdle light, 

 tessellated with dark bars opposite the sutures, 

 the scales smooth, as in /. smaragdimis. Valve i 

 with 10, ii to vii with 1-1, \'iii with 9 slits. 

 Length 10-5-14, breadth 5-7-5 mm. 



Hah. — Marino, St. Vincent's Gulf, in pools at high-water mark, on 

 smooth pebbles ; Cape Spencer, Investigator Strait, under similar con- 

 ditions, within the influence of the surf (Matthews). It is named in 

 honour of Mr. H. Thomas, who has executed excellent drawings of 

 this and other South Australian Chitons. 



Ischnochiton Thomasi, 

 n.sp. 



