TONICIA. 195 



pectinated insertion-plates. The genus Onithochiton has similar 

 smooth valves, but the posterior valve lacks slits and teeth of 

 insertion. 



The species of Tonicia inhabit mainly the shores of the southern 

 and tropical Pacific, being found from Middle America to Cape 

 Horn, and from the Philippines to Australia and New Zealand. 

 They may be grouped thus : 



A. Valves not immersed or separated, imbricating, section Tonicia. 



1. Species of West America. 



2. Species of the West Indies. 



3. Species of New Zealand, Australia, Red Sea, Philippines. 



B. Valves partly separated, the girdle encroaching on them at the 



sutures, section Fannettia. 



Section Tonicia s. sir. 

 1. Species of West American shores. 



T. CRENULATA Sowerby. PL 45, figs. 69, 70, 71, 72. 



Shell oblong-ovate, slightly more narrowed in front, moderately 

 raised, the back carinated. Ground-color buff or slightly rose- 

 tinged, having oblique dark olive irregular stripes, often marked on 

 some valves with rich brown ; apices of valves pink when eroded. 



The lateral areas are raised and well-defined, and except the pos- 

 terior third or fourth, are studded closely with black eyes; the suture 

 is prominently and coarsely crenulated, and there are some irregular 

 radiating rows of granules on the back part of the areas, and some- 

 times a row or two dividing the eye tract. Central areas having a 

 smooth keel in the middle, bounded on each valve by a V formed by 

 two low divergent waves, crossed by convergent riblets ; pleura or sides 

 sculptured with longitudinal-diverging rugae or ribs. Anterior 

 valve high, with radiating rows of weak granules alternating with 

 rays crowded with eyes. Tail valve with slightly posterior, elevated 

 mucro. 



Interior white, with a large red tract in each of the median valves. 

 Slits in anterior valve 8, central 1, posterior 14; teeth obtuse and 

 short in the posterior, acute and longer in the anterior valves, sulcate 



