502 SNODGRASS AND HELLER 



natural agencies. The land fauna is very scant and its rela- 

 tionships have not yet been determined. Besides birds a lizard, 

 Lagosoma erundeli, occurs there ; also an Agrionid dragonfly, 

 a Cicindelid beetle and a very few Diptera. The nymphs 

 of the dragonflies live in the brackish lagoon inside the circu- 

 lar coral bank. No land plant is native to the island, and the 

 birds and crabs are everywhere so abundant that no plant could 

 possibly grow there unless artificially protected. 



The island is roughly circular, being composed of a narrow 

 ring formed of sand and pieces of coral. Its width varies 

 from 200 to 1,300 feet, averaging in most places between 300 

 and 600 feet. The interior of the island is occupied by a 

 lagoon of brackish water full of algge. According to P. J. 

 Henning's chart of Clipperton Island, made in 1897, its depth, 

 near the center is forty fathoms, and at one point south of the 

 center, fifty-five fathoms. Everywhere near the shore it is 

 shallow, but the bottom slopes off very irregularly toward the 

 center. The depth varies slightly, probably according to the 

 rainfall, for the lagoon was, in 1898, entirely shut off from the 

 ocean. According to Henning's chart the water over a reef in 

 the middle of the lagoon is only from two to eight inches deep. 

 During our visit in November, 1898, the reefs were everywhere 

 two feet, and in most places much more, beneath the surface of 

 the water. This reef crosses the middle of the lagoon in a 

 northwest-southeast direction along the line of the greatest 

 diameter of the atoll. Near the northwest shore of the lagoon 

 are several small islands on which one of the terns of the 

 island. Sterna fuUginosa^ was nesting in great numbers during 

 our visit. 



The height of the island is uniformly very low and its surface 

 flat, except on the outer side where it slopes off rather steeply 

 to the ocean, and on the inner side where it slopes more gently 

 to the lagoon. Everywhere, except at one place to be men- 

 tioned later, it is composed of irregular fragments of coral 

 stems. Where sections of the banks have been cut by water, 

 the material below the surface is seen to be exactly the same as 

 that at the surface, except that it is compacted into solid beds. 

 No coral sandstone rocks were found. The pieces of coral 



