or undulatiDg. Toward the outer edges the wrinkles become 

 ler and more separated. End valves sculptured with radiating 

 riblet> : posterior valve having the macro central. Interior white, 

 the end valves usually marked with a brown crescent; sutural lobes 

 rounded ; sinus wide and flat. Anterior valve having 12, median 

 valves 1, posterior valve 12 slits; teeth smooth, rather .-harp. 

 Kaves solid. 



(iirdle covered with flattened striated scales, which are verv 

 unequal in si/.c, but become larger toward the valves (fig. 21). 



Length 32, breadth HI mill. 



Australia, 



The texture of the shell is peculiar, the outer layer being thin 

 and easily broken through, exposing an extremely spongy layer. 

 ( arpenter's specimens seem to have been worn so as to expose this 

 layer in places, hence the name cariosus. In the normal and un- 

 worn specimens before me the outer surfare is scarcely carious 

 though dull and uneven, nor are the eaves spongy. Carpenter's 

 original description is as follows: 



Heterozona cariosa (pi. 24, fig. 23). Shell subelongate, rather 

 elevated, the jugum rounded. Mucro median, moderately elevated ; 

 whitish-ashen, slightly variegated at the sutures occasionally. 

 Central areas very granose in a young specimen, the granules 

 minute and close toward the jugum, then becoming rugose lines, 

 undulating anteriorly, and widely separated on thesides; the adult 

 shell is carious. Lateral areas having 3-8 deeply but irregularly 

 granose radii, the grains at the sutures large; end valves having 

 30-40 graniferous radii. Interior: posterior valve with 11, central 

 1, anterior valve 11 slits. Teeth acute; eaves wide, spongy; sinus 

 large, flat, smooth. Girdle (pi. 24, fig. 23), clothed with nornal 

 striated imbricating scales and having long, large striated solid 

 scales scattered here and there. (Qt?r.) 



Length 30, breadth 161 mill., divergence 100. 



Australia (Mus. Cuming No. 46). 



This shell forms an exact transition between Ischnoplax and the 

 true Ischnoehiton. The mantle resembles Ischnoplax in its double 

 series of scales ; although if the large ones were plucked out, the 

 latter would be nearly of a normal arrangement, except that they 

 aiv rather nariow a- in /. castns. It differs from 7>r///>oy,A/.r, not 

 only in not lu-in^ narrow and elongated, but in having a normal 

 IIMKTO. The species is curiously like Stciiormltn'n magdalenentis, 



