PANAMIC-PACIFIC PELECYPODA 23 



South of the Paita Peninsula and between it and the third major 

 headland of the coast, that of the Illescas Peninsula, is the large open Bay 

 of Sechura. Like its much smaller neighbor to the north (Bay of Paita), 

 the outline of its shore is shaped like that of a large fish hook, its sharp, 

 barbed end at Punta Aguja pointing northwest, its long shank forming 

 the seaward margin of the great Sechura desert stretching far inland. At 

 both its northern and southern ends, the shores of Sechura Bay are rocky 

 lined with high, steep cliffs; in between the long stretch of the inner bay 

 is an open sandy beach. Bayovar at the south end, is a small, abandoned 

 settlement, at one time the port and terminus of a small railway to some 

 sulphur deposits at Revantazon at the southeast end of the Illescas 

 Mountains. West of Bayovar towards Punta Aguja, the shore is rugged, 

 formed for the most part of schist and other metamorphic rocks. 



The beach at Bayovar is generally strewn with shells, many species of 

 which attain a larger size here than they do in the north. This condition is 

 well illustrated by Mexicardia frocera which often has a height of 100 mm. 

 or more. The beach is also covered with the dead valves of Anomia peru- 

 viana, large banks of which must lie off shore. Aequipecten purpuratus is 

 as large here as so commonly seen south of Lima. During the severe aguaje 

 of 1925, the shore at Salinas was swept by strong waves and large quantities 

 of marine life of all sorts cast upon the beach. Many seabirds, deprived of 

 their normal source of food, died in large numbers or wandered around on 

 shore in a starved condition. 



4. FAUNAL PROVINCES 



Using the mollusks as a basis. Woodward, a century ago, arranged the 

 coastal or shallow-water faunas of the eastern Pacific into five main geo- 

 graphic provinces, his data for the most part being the list of species com- 

 piled by D'Orbigny. Dall in 1910, followed Woodward's classification with 

 only a few, minor changes. In 1936, Schenck and Keen suggested some 

 modifications of the same system for the west coast of the United States, 

 and placed the main boundaries at somewhat different points. They further 

 indicated that the faunal provinces were not so sharply limited as first 

 believed but were separated by wide belts of overlap or transition in which 

 the species were more or less mixed. It will be seen later that an overlap or 

 transitional zone separates the tropical Panamic-Pacific fauna from that of 

 the cooler water Peruvian fauna along the northwest coast of Peru. Detailed 

 studies along the Pacific coast of Central America and South America may 

 perhaps show the need for other modifications or for the recognition of sub- 

 regions, as for instance around the Galapagos Islands. 



From the north southward, the main faunal or zoogeographic provinces 



