20 NASSA. 



Marrat, is the lyrate form ; JV. tricarinata, Lam., is the carinated 

 form; N. wulpta, Marrat, is another; JV. sistroides, Nevill, N. 

 trinodosa, Smith, and N. corticata, A. Ad. Another variety 

 occurs, showing a close affinity with the N. muricata, Quoy and 

 Graim., and the shell figured in Reeve's Conchologia Iconica as 

 the N. vibex, Say, is a spiny form. Some of the shells from 

 Ceylon are very closely connected with varieties of the N. 

 Gruneri, D linker, and others with smoother ribs to the JV. Jack- 

 soniana, Quoy and Gaim. 



" We may name these shells and describe them as distinct, but 

 they will not be so after we have finished; on the contrary, we 

 may adopt another plan and name them varieties, but the same 

 objection continues; the variety we have named as coming from 

 any locality will be found to differ from the shells brought up 

 from the same ground by the next haul of the dredge. It is a 

 very disagreeable task to be compelled to state that the starting- 

 point of the systematist, upon which the whole- fabric is built 

 up, is wrong, and the whole of the deductions drawn from this 

 source are erroneous; nevertheless I am compelled to utter that 

 which I believe to be strictly and unquestionably true. I can- 

 not expect that conchologists who are totally unacquainted with 

 the materials upon which I have based my deductions, will 

 coincide with my views. If they had obtained a knowledg- 

 the whole of the figured or described species of Xassa, they 

 could not by this plan follow the intricate passages revealed by 

 the study of variation. It is not by an intimate knowledge of 

 the described species that these facts are elicited, but it depends 

 upon a knowledge of the innumerable intermediate forms which 

 diverge from them in every direction as to how these deductions 

 are to be drawn. 



" In a long series of forms, commencing with shells represent- 

 ing the largest specimens in the genus, these can be traced with 

 unerring certainty into others, forming the smallest examples 

 known to exist; again, the broadest varieties can just as easily 

 be connected with others that are the narrowest examples in the 

 group; and every grade of difference throughout the long lines 

 of progressive variation is distinctly seen. In the case of the 

 shells having smooth forms, such as A". f/m.s, Linn., the varieties 

 may not be all smooth specimens, but they may vary into costate 



