1 "Beitrag zur nÄheren Kenntniss der Sudamerikanischen Alligatoren," 'Annalen des Wiener Mus.,' Band i.

2 According to Natterer, the dental formula of J. nigra and J. fissipes is ^18-18/_18-18, of J. sclerops ^19-19/_20-20, of J. callifrons and J. punctulata ^20-20/_18-18.

3 By this term I denote that squarish flat area bounded by the postfrontal and squamosal bones laterally, by the occiput posteriorly, and by a line joining the outer angles of the postfrontals anteriorly.

4 The greater proportional length of the symphysis is noted by DumÉril and Bibron.

5 In a skull of this species 14¹/₂ inches long, in the British Museum, the vomers are completely excluded from the palate, and their anterior ends do not extend for an eighth of an inch beyond the palatine part of the palato-maxillary suture, which lies on a level with the anterior margin of the twelfth alveolus. Each vomer is 2³/₈ inches long, and presents the same general form as that of Jacare; only the anterior division is but a very small, flat and thin plate, not a quarter of an inch long. The boundary of the median nares is formed in equal proportions by the vomer and the palatine, and is opposite the fourteenth tooth. The hinder end of the vomer articulates with the end of the descending process of the prefrontal.

6 'Catalogue of the Tortoises, Crocodiles, and AmphisbÆnians in the Collection of the British Museum,' 1844, p. 59.

7 Or it is possible that the Rhynchosuchus from New Guinea, which I have examined, is specifically distinct from the Bornean form.

8 The second and third cervical rows in Caiman palpebrosus and trigonatus also contain a median scute, and consequently an odd number of scutes. In Caiman trigonatus, the third to the ninth supra-caudal rows have each a median single scute.

9 The suspicion above expressed has been fully confirmed by observations made by Mr. J. J. Bennett, the Secretary of the Linnean Society. Mr. Bennett informs me that, in an aquarium in his possession, an Astacus fluviatilis has twice cast its shell, and the process of moulting was on each occasion accomplished without any splitting of the shell at the joints of the claws.