ISCHNOCHITON. 93 



I. CONTRACTUS Reeve. PL 23, figs. 81, 82. 



Shell oblong, peculiarly contracted at the extremities 

 especially the anterior; terminal valves and lateral areas of 

 the rest concentrically granulated, granules solitary, central 

 areas very minutely and closely ridged, ridges curved and con- 

 spicuous towards the sides, finer towards the middle and decussated 

 with oblique stride ; light bay, flamed in the middle with brown ; 

 ligament granosely coriaceous, dark brown. (Rve.) 



Tasmania (Mus. Cuming) 



Chiton coniractus REEVE, Conch. Icon. 1. 15, fig. 78, March, 1847. 

 Chiton decussattis REEVE, Conch. Icon. t. 18, f. 107, April, 1847. 

 Chiton castus RVE., t. 22, f. 145, May, 1847. Ischnochiton 

 castus CPR., MS., and 1. intergranosus CPR., MS. Lepidopleurus 

 speciosus H. AD. & AN GAS, P. Z. S. 1864, p. 192 ; 1. c., 1865, p. 187. 



This species has been several times described, but the range of 

 variation seems to be less than in some other allied forms, although 

 the coloring varies considerable. The acute dorsal ridge, divergent or 

 zigzag sculpture of the dorsal areas, the granulation of the lateral 

 areas and serration of the sutures are characteristic. The descrip- 

 tions of the several forms included under contractus follow below. 



Carpenter's notes are as follows: shell oval, subelevated, ashy, 

 irregularly streaked with brown-olive. Otherwise like I. castus, 

 but the central areas are everywhere zigzagly wrinkled, the lines 

 which in castus are conspicuously at right angles to the diagonal 

 line are not seen in contractus. Lateral areas and end valves hav- 

 ing close radiating wrinkles, more or less broken into granules con- 

 centrically, sometimes scarcely at all, sometimes entirely so. Inte- 

 rior: anterior valve having 14, central valve 1, posterior valve 13 

 slits; teeth acute; eaves conspicuous, hardly spongy; sinus wide, 

 flat, smooth ; it appears broader and the sutural laminae not so high 

 as in castus. Girdle pale black-brown ; scales as in /. castus. 

 Length 37, width 17* mill.; divergence 110. 



There are 3 specimens in the Cuming collection, from Tasmania, 

 and two on the same tablet which are really an intermediate variety 

 of I. castus. I cannot see the contracted shape figured by Reeve, 

 in either of the specimens, which are shaped just like /. lonyicymba. 

 The streaked coloring is quite exaggerated ; it is very irregular, not 

 in even lines as in Reeve's figure. The divergence is the same as in 

 I. casius. Side by side they exactly correspond. The difference 



