ISCHNOCHITON. 87 



Section Ischnochiton s. str. 

 (1.) Group of I. longicymba. 



Oblong species, with fine, not conspicuous, sculpture, the central 

 areas granulated in quincunx or in zigzag pattern, lateral areas 

 radially ribbed. 



The species are from Australo-Zelandic seas. 



I. LONGICYMBA Quoy & Gaimard. PI. 22, figs. 58-66. 



Shell oblong, rather highly and broadly arched, not in the least 

 carinated. Surface to the naked eye appearing smooth on the cen- 

 tral, radiately lirulate on the lateral areas and end valves. Color 

 extremely variable, usually pale olive mottled with dark olive or 

 purple-black, or having a broad light band along the back. 



Lateral areas distinctly raised, sculptured with 8-12 radiating 

 riblets, often bifurcating, the intervals densely granulated ; the rib- 

 lets are interrupted by irregular impressed concentric growth-lines. 

 Central areas very closely and finely granulated in quincuncial 

 pattern ; the granulation is nearly even on the jugum, although the 

 anteriorly divergent rows of granules are sometimes slightly more 

 prominent ; on the slope between central and lateral areas, and on 

 the extreme sides of the latter the granules are arranged to form 

 more or less distinct longitudinal rows. The end valves are very 

 minutely granulated and radially lirulate. Umbo of posterior 

 valve rather low, obtuse ; posterior slope visibly concave. 



Interior green or blue sometimes varied with red or corneous. 

 Anterior valve with 9-12, central 1, posterior valve 11 slits; teeth 

 thin, sharp and smooth ; posterior tooth of the side insertion plates 

 short, and terminating abruptly before attaining the posterior mar- 

 gin of the valve (figs. 61, 64) ; eaves solid. 



Girdle closely covered with solid, convex but somewhat flattened 

 imbricating scales, most of which are rather weakly striated, but 

 among which non-striated scales are mingled (pi. 22, figs. 63, 66). 



Length 33, breadth 16 mill, (often smaller). 



New Zealand : Auckland to Dunedin ; Pitts' Island; Auckland 

 Is. ; Campbell Id. 



C. longicymba (? Dufresne, Mus. Paris; Blainville, Diet, des Sci. 

 Nat. xxxvi, p. 542), QUOY & GAIMARD, Voy. de PAstrol. Zool. iii, 

 p. 390, t. 75, f. 1-18 (1834). REEVE, Conch. Icon. t. 19, f. 125, t. 

 24, f. 163d. Lepidopleurus longicymbus HUTTON, Man. N. Z. 

 Moll. p. 113 (1880). 



