ONITHOCHITON. 247 



The sculpture in this form differs markedly from the Australian 

 and S. African species. 



O. SEMISCELPTUS Pilsbry, n. sp. PI. 55, figs. 10, 11. 



Shell oblong, elevated, subangular, dark olive-green, having snowy 

 angular lines and dots on the lateral areas, and closer, more regular 

 transverse lines on central areas. Surface shining and smooth on the 

 central areas, closely and finely striated radially on the head valve and 

 lateral areas, the^trice crowded and subgranose, about 12 in number 

 on each lateral area. Interior white. Girdle narrow, brown. 



Length 27*, breadth 16 mill.; divergence about 95. 



Habitat unknown. 



This species resembles the stout, elevated, dark olive forms of 0. 

 undulatus, such as occur at Auckland, N. Z., in contour and colora- 

 tion. It differs markedly from undulatus and all other known 

 species in the sculpture of the lateral areas. 



Figure 10 shows two half valves, the upper illustrating the color- 

 pattern, the lower the sculpture. 



O. LYELLII Sowerby. PL 55, figs. 1-7. 



Shell oblong, moderately elevated, the dorsal ridge rounded or 

 slightly subangular. Color extremely variable ; typically green at 

 the sides, with a tessellated black or chestnut dorsal stripe in the 

 middle of a pink-dotted area ; but other specimens are blotched with 

 green at the sides with concentric creamy lines and a creamy area on 

 the ridge of each valve, along which runs a band of dark chestnut 

 spots often on a bluish ground. Occasional specimens have a large 

 black blotch on the sides of some valves. 



The median valves are beaked. Lateral areas a trifle raised, 

 sculptured with rather uneven concentric shalloiv grooves with rather 

 wide, flat interspaces ; near the front edge of each lateral area there 

 is a narrow band of minute eye-dots. Central areas sculptured at 

 the sides with fine, close grooves (continued from those of the lateral 

 areas) converging toward the ridge, where there is a narrow smooth 

 dorsal band. Anterior valve having about 10 narrow rays of eyes, 

 the spaces between sculptured with concentric grooves interrupted 

 by the eye-bands into scallops having their convexity upward. Pos- 

 terior valve broadly triangular, depressed. 



Interior white with a crimson spot in the cavity of each valve. 

 Sinus deep, angular, delicately subdenticulate. Anterior valve hav- 

 ing 8, median 1 slit ; the teeth rather long, sharply pectinated out- 



