NOTICE. 



In the long interval since the publication of the first part 

 of this Manual, materials have so accumulated on the writer's 

 hands, that it has been found impracticable to condense them 

 within the space at first contemplated. The illustrations also 

 have been more numerous than was originally expected, and 

 occupy considerably more room. But although a Supplement 

 has become inevitable, the publisher has allowed an extra 

 number of pages, in order to render the present part complete in 

 itself. The writer hopes to make the Appendix more valuable 

 by figures and descriptions of the animals of many hitherto un- 

 described Bivalve genera, the materials for which have already 

 been placed at his disposal by Dr. J. E. Gray. The present 

 part owes much to the assistance of Mr. Albany Hancock, of 

 Newcastle; Mr. Thos. Davidson, F.G.S., and Mr. T. H. 

 Huxley, P.E.S. 



