EXPLANATION OF PLATE XVIII. 
Fig. 1. Ambonychia ? poststriata, Eth. fil. Fight valve exhibiting the 
elevated urnbone, posterior radiations, and concentric laminae. 
„ 2. Anterior end of the same specimen showing the large byssal sinus 
[The figures, from drawings by Mr. G. H. Barrow, of the Australian 
Museum, are of the natural size.] 
