12 MANUAL OF IflE M0LLXJ8CA. 



and they are the ornaments of barbarous tribes. The Friendly- 

 Islander "wears the orange-cowry as a mark of chieftainship 

 {Slutclibury), and the New Zealander polishes the elenchus into 

 an ornament more brilliant than the "pearl ear-drop" of 

 classical or modern times. [Clarke.) One of the most beautiful 

 substances in nature is the shell-opal, formed of the remains of 

 the ammonite. The forms and colours of shells (as of all other 

 natural objects), answer some particular purpose, or obey some 

 general law ; but besides this, there is much that seems specially 

 intended for our study, and calculated to call forth enlightened 

 admiration. Thus the tints of many shells are concealed during 

 life by a dull external coat, and the pearly halls of the nautilus 

 are seen by no other eyes than ours. Or descending to mere 

 " utility," how many tracts of coast are destitute of limestone, 

 but abound in shell-banks which may be burned into lime ; or 

 m shell-sand, for the use of farmers.* 



Not much is known respecting the individual duration of the 

 shell-fish, though their length of life must be yery variable. 

 Many of the aquatic species are annuals, fulfilling the cycle of 

 their existence in a single year ; whole races are entombed in 

 the wintry tide of mud that grows from year to year in the beds 

 of rivers, and lakes, and seas ; thus, in the "Wealden clay we 

 find layer above layer of small river-snails, alternating with 

 thin strata of sediment, the index of immeasm^ably distant 

 years. Dredgers find that whilst the adults of some shell-fish 

 can be taken at all seasons, others can be obtained late in the 

 autumn or winter only; those caught in spring and summer 

 being young, or half-grown ; and it is a common remark that 

 dead shells (of some species) can be obtained of a larger size 

 than any that we find alive, because they obtain their full 

 growth at a season when our researches are suspended. Some 

 species require part of two years for their full development ; 

 the young of the doris and eolis are born in the summer time, 

 in the warm shallows, near the shore; on the approach of 



because they have induced vo}'agors to collect. Mere shell-collecting, however, is no 

 more scientific than pigeon- fancying, or the study of old china. For educational pur- 

 poses the best shells are the types of genera, or species which illustrate particular 

 points of structure ; and, fortunately for students, the prices liixve been much diminished 

 of late j'ears. A C«n>i/7r/a, once " worth 100 guineas" (Sowerby), is now worth Is. 

 only; a wen tie-trap whicli fetched 40 guineas in 1701 (Rumphius) was worth only 

 20 guineas in 1753, and may now be liad for bs. The Conns gloria-mar is has fetched 

 £50 more than once, and Cypraa umbilicata has been sold for £30. 



* Shell-sand is only beneficial on peaty soils, or heavy clay land. It sometimes 

 hardens into limestone, as on the coast of Devon ; and at Guadaloupe, where it con- 

 tains littoral shells and human skeletons of recent date. 



