ends almost in a point, 6-1/4 inches behind its anterior end. The posterior edge of the vertical plate is extremely thin, and 7/8ths of an inch deep. It articulates with the anterior end of the vertical plate of the pterygoid, while the straight inferior edge articulates throughout with the palatine plate of the palatine bone. The vomers terminate midway between the median nares and the descending process of the prefrontal. The median nares are bounded entirely by the vomer and the maxilla. They correspond with the nasal face of the palato-maxillary suture, but are rather behind its palatine face, and they are about on a level with the interval between the tenth and eleventh teeth. If the anterior edge of the palatine bone bounded them, they would be a little behind the twelfth tooth. The posterior nares, 2-1/8 inches wide, by 7/8ths of an inch long, look altogether downwards, are completely divided by a bony septum, and have the form of a rhomboid with its narrowest side posterior. They are surrounded by a strong raised ridge, incomplete only at the anterior and outer angles of the rhomboid. Five species of _Jacare_ are enumerated by Natterer--_J. fissipes_, _J. sclerops_, _J. nigra_, _J. punctulata_, and _J. vallifrons_. They have met with only in South America. [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. * * * * * II. In the family of the CROCODILIDÆ the teeth are usually strong and very unequal in size, and there is always a considerable difference between the anterior and the posterior teeth. The two anterior mandibular teeth are received into pits in the premaxilla; but the canines pass into grooves (which may be converted into fossæ) situated at the junction of the premaxilla and maxilla. The other mandibular teeth are received between the maxillary teeth. The symphysis of the lower jaw does not extend beyond the level of the seventh or the eighth mandibular tooth. The premaxillo-maxillary suture may be either straight or strongly convex backwards. The divided vomers do not appear in the palate. The posterior nares look more or less backwards, and are transversely elongated. The supra-temporal fossæ are always open, and the feet are distinctly webbed. The dorsal scutes are not articulated; and there are no ventral scutes. Two genera, _Crocodilus_ and _Mecistops_, are distinguishable in this family. Genus 4. CROCODILUS.