PANAMIC-PACIFIC PELECYPODA 9 



the lower taxa must also be divided, and often new ones proposed. This 

 condition has been the case in the Arcidae, Veneridae, and the Olividae. 

 Other large families are more compact, such as the Tellinidae and Conidae, 

 and efforts to divide them even into clearly defined genera have been less 

 successful. The author is strongly opposed to name changing for mere 

 priority reasons or to give undue recognition to works of questionable 

 value, thereby replacing generic names well established by long usage and 

 scientific authority. 



2. HISTORICAL REVIEW 



The collecting of plant specimens, mainly for the purpose of discrimi- 

 nating those with food or medicinal value began shortly after the Spanish 

 Conquest, but the first serious studies projected along modern scientific 

 lines in tropical America was that of the French Mission sent out by the 

 Academie des Sciences in 1735-44 for the purpose of obtaining an exact 

 measure of a degree of the meridian at the equator and from which the size 

 and figure of the earth could be calculated in conjunction with observations 

 of a similar character at other points of the earth's surface. Members of 

 this mission included C. M. de la Condamine, Pierre Bouguer, and Louis 

 Godin as geodesist and Joseph de Jussieu as botanist. No marine shells 

 were obtained by this group. This mission was followed in the opening years 

 of the 19th century by the famous journey of Alexander von Humboldt 

 and Aime Bonpland who travelled through the greater part of northern 

 South America from eastern Venezuela to Peru. No other expedition to 

 South America accomplished so much in the whole realm of science or left 

 as lasting impression of good will in the lands through which these distin- 

 guished visitors journeyed. During the last stages of this remarkable expedi- 

 tion, Humboldt and Bonpland traversed southern Ecuador and reached the 

 upper Amazon or the Maranon at Tompenda situated above the cataracts 

 known as the Ponga de Retema. This was a point of some geographic 

 significance because of an earlier astronomical fix made by Condamine. 

 From this place on the upper Amazon, Humboldt and Bonpland began 

 the ascent of the Peruvian Andes which they crossed in the latitude of 

 Cajamarca and Cotumaza and finally reached the coast at Trujillo from 

 which point they continued on southward to Lima. As the two travellers 

 descended the last slopes of the Andes and approached the coast, they 

 entered into a strange land which became increasingly more arid, 

 the slopes of the mountains beyond the narrow limits of the valley floor 

 devoid of plant growth aside from a few straggling bushes and cacti. This 

 was the travellers' introduction to the great coastal desert of Peru which 

 begins in the north near the Ecuadorian border and extends far southward 

 into middle Chile. Gaining the coast, they noticed that the air held a feeling 

 of coldness, the sky overcast, and the nearby landscape at times obscured 

 by a blanket of mist (garua) which drifted inland from the sea, tainted 

 with a scent of ammonia arising from offshore rocks and islands, whitened 

 with guano. Humboldt speculated deeply on this unusual climatic set-up 



