The Crocodilia of British Guiana consist, apparently, of four species of Caiman, of which only the black caiman, C. niger, reaches a large size and is supposed to be dangerous to man. The smaller species were studied in three regions: (i) in the jungle some forty miles from the coast; (2) in the parks and sugar estates in the neighborhood of Georgetown; (3) along the rivers and irrigation canals of the " savannas," or level plains, in the eastern part of the colony. As the chief object of the expedition (for which the writer is indebted to the Carnegie Institution) was the collection of embryological material, especial attention was paid to the nesting habits of the caimans. In the first habitat mentioned above no nests were found, and but few animals. This might have been expected from the character of that region. The jungle comes right down to the water's edge (the Essequibo River and its tributaries), with few swamps and water holes such as are attractive for breeding grounds. The rivers are so swift that canoes follow the irregularities of the shore rather than fight the stronger current of the midstream. The adult caiman would have no difficulty in swimming against such a current, but the newly hatched animals would probably be gradually borne toward the sea. Farther inland the black caiman is said to abound, but what the character of the habitat may be in those regions the author is unable to say from personal observations. In the region about Georgetown the caimans are much more common. In the beautiful botanical gardens, of which the colony is justly proud, are numerous ponds and canals of fresh water, often surrounded and overhung by trees and btnshes, and with the surface of the water more or less covered with Victoria regia (anlazonica) and other aquatic plants (fig. I). In such a body of water a floating crocodilian can be distinguished only with the greatest difficulty, the protective resemblance is so marked. On the shores of these ponds and on the islands found in them are built the nests of the caimans, to be described later. In the trees and bushes surrounding and overhanging the water are heron and other rookeries, where hundreds of birds, both old and young, may be seen. Doubtless young birds that fall into the water, and old birds that often stalk about on the huge lily pads, may frequently serve as food for the hungry crocodilians that lurk in the water. The ponds in some places are fairly free from vegetation, in other regions