yo.nv>. SYNOPSIS OF THE VENERIDM—DALL. 337 



the temperate and ))oreal re^-'ions, beloiioinu- to twelve o-j-onps, of which 

 Sa.i'!d<»jnis and Px, ph'idhi have no representatives known in ouf trop- 

 ical waters. The Tropics in America have representatives of twenty- 

 nine groups, of which T'lvcJa and Chiouc are the most prolific in 

 species; none of the other groups exceeds four species. In individuals 

 the groups of the Temperate Zone seem to be most prolific, such as 

 Yoiux, PrototJiaca^ Saxidonixs^ and Agriopohid^ and fi-om these the 

 greater portion of the food supply derived from meintiei-s of this 

 family by man is obtained. 



The southern limit of the tropical fauna on the west coast of South 

 America is near Payta, Peru. On the east coast it descends at least as 

 far as Rio de Janeiro, its northern limit reaching the latitude of Cape 

 Hatteras offshore and Cape Canaveral on the actual coast. On the 

 west coast the temperate fauna meets the northernmost extension of 

 the tropical fauna near Point Conception, California. The northern 

 limit of the strictly temperate-region fauna, on the west, is the line of 

 floating ice in winter in Bering Sea, about the latitude of the Pribilof 

 group of islands. On the east we may put the boundary near Cape 

 Breton Island, but, owing to the inshore polar current on this side of 

 the continent, the arctic species reach farther south and the census of 

 the temperate fauna is more meager than on the more favored north- 

 west coast of the continent or the western shores of Europe in the 

 same latitude. 



The recognizable ancestry of the Veneridte appears in the Upper 

 Cretaceous or Lower Eocene. No true Yenerid, in the strict sense, 

 apjjears before the Tertiary. The modifications followed through the 

 successive horizons are most interesting. Thus, in the Oligocene we 

 have Ihj])hant<)S(nn<i with fine zigzag chiseling of the surface. In the 

 Pliocene this sculpture is obsolete and its traces hardlvto be found. 

 The recent type has a smooth surface, but when attacked by decay the 

 manner in which the shell weathers reveals the zigzag internal struc- 

 ture hidden under an apparent!}' normal, smooth exterior, and the 

 color-pattern frequently follows a zigzag lineation which is no longer 

 expressed in terms of sculpture. 



The beauty of the shells has led in some cases to a traffic in them by 

 means of aboriginal trade. Thus Ilyderoconclia was long carried to 

 the Orient by the Lascar crews of ancient Spanish galleons, and this 

 has led to wrong ideas of geographical distri])ution. Jlcretrl.i' is a 

 favorite with the Chinese and Japanese, not mereh' as a source of food 

 or ornament, but is incorporated into lacquer work and imitated in 

 porcelain or ])ott(^ry. The conunon Yenu!< of our own eastern coast 

 was the source from which the Dutch and Indians prepared their shell 

 money or wampum and ceremonial ])elts. A south European species 

 in ancient times was the eml)lem of Aphrodite, and in the South Seas 

 species of Veuerid^ were largeh^ used for personal adornment. 



