is NASSA. 



round pellot; iindor tliis tlic (n-eature conocals itself. The fry 

 twist and twirl about l\v means of their ciliated lobes. N. 

 Dititabiliti is an article of food in Italy, The generic name is 

 that of a narrow-necked wicker basket used for catching; fish, 

 and in such a basket,, lobster pots, etc., the iV^a.s.sY/, itself is 

 frequently caug^ht, attracted thither by odors savory. 



iVa.ssa reticaiata is said to be very destructive in the 03'ster 

 pares of Arcachon (S. of France). It is so numerous that a 

 single tide has yielded 14,(500 specimens within a space of 40 

 French hectares (= about 100 acres). The adult Naaaa will 

 l)ore tiirough the shell of an oyster three 3'ears old, within eight 

 hours ; but the young shells are far more destructive because 

 they select the tender shells of tlie very 3'oung oysters, some- 

 times piercing fifteen or twenty in succession before their 

 hunger is satisfied. An oyster a month old is destroyed in a 

 half hour.* 



One of the best students of the genus Nassa is undoubtedly 

 Mr. F. P. Marrat, of the Liverpool Museum. f Iml)ued with 

 extreme development views he has, unfortunately, adopted the 

 principle in his scientific work that, the variations of species 

 being illimital)le — species in fact, as usually defined, being non- 

 existant, the naturalist may apply a specific name for each 

 modification of form, sculpture or coloration ; a principle the 

 absurdity of whicli must be ai)parent when it is considered that, 

 no two shells being exactly alike, it will admit of the description 

 of every individual specimen as a " new form." Mr. Marrat has, 

 however, fully demonstrated the insufficiency of distinctions 

 based on sculpture in a number of species of the genus; a result 

 most confusing to the systematist,and which leaves the validity 

 of many forms described from single or few specimens very 

 (luestional)le. 1 am tempted to mtdce some extracts from Mr. 

 Marrat 's latest paper,^; the subject of variation being sufficiently 

 important in a general sense to justify me in devoting a few 

 lines to its illustration in this particular genus. 



* Soubeiran, IJiill. Soc. d'AcclimritaLioii, 2 Ser., iii, ;J, 1866. 



t "On the variation of sculpture exhibited in the shells of tlie genus 

 i\ra«««." " On forty proposed new forms in the genus Nussa," etc. 



\ " On the Varieties of the Shells belonging to the genus iVrtS9rt." 



