102 



26. ISCHNOCHITON VERCONIS, Sp. nOV. 



Plate xxiv., figs. la,b,c,d,e,f. 



Mr. Hedley says: "This is certainly a new species and a 

 magnificent one. One would need to disarticulate a valve 

 to be sure of the classification. Probably it is an Ischnochi- 

 ton, and perhaps of the section Ischnoradsia." As only one 

 specimen was found I am not disarticulating, but hope to 

 supplement my description later. 



General Appearance. Shell elliptical, flattened, side 

 slopes curved. Colour, uniformly slatish-grey, tending to 

 heliotrope. Girdle and valves of the same colour. 



Anterior Valve. No very distinct markings. Surface 

 rough with irregular concentric growth lines and minute 

 longitudinal striae. Eight teeth. 



Posterior Valve. Mucro-median, prominent; divided 

 into two distinct areas by a slightly-raised riblet running up 

 to the mucro. The anterior half has longitudinal colour 

 markings with microscopic nodulose lines. To the unaided 

 eye it seems smooth. The posterior half has concentric 

 irregular nodulose lines similar to the anterior valve. 



Median Valve. The pleural and dorsal areas run 

 together, while the lateral area is very distinct. The dorsal 

 area is smooth, horny, with brown-pencilled longitudinal 

 lines and microscopic zigzag striations. The pleural area has 

 very delicate longitudinal markings. The lateral area is dis- 

 tinctly raised and has a lighter shade of colour than the 

 pleural. The very slight longitudinal and lateral markings 

 give it a textile appearance. 



Girdle. Clothed with imbricating scales, curved, apices 

 sub erect; under the microscope the scales are beautifully 

 frosted over and show about ten transverse parallel grooves. 

 The girdle is one-third of the depth of the lateral area, 

 about 3 mm. across. 



Interior. Bluish-grey colour with broad sinus and dark 

 splashes near the sinus of each valve. The anterior valve 

 has delicate brown pencillings from the sinus to half its 

 depth with eight riblets. 



Measurement. Dried specimen. Length, 44 mm. ; 

 breadth, 28 mm. 



Habitat. Rockpool, inside reef, Ellenbrook, south of 

 Cape Naturaliste, Western Australia. 



Remarks. It is different in shape from any Australian 

 Ischnochitons, and the only specimens in my collection of 

 similar shape are Mopolia h/nosa, Gould, from California,, 

 and Chiton Magnificus, Deshayes, from the Philippines. This 

 species has been named after Dr. Verco, to whose generosity 



