1934J Halt, African Manatees 551 



form of a double, symmetrically notched circle. The posterior nares of 

 senegalensis are very nearly circular, whereas those of manatus are deltoid. 



The pterygoid process of the manatees is formed by wings of the 

 alasphenoid, palatine, and pterygoid bones, and this compound process 

 usually ends distally in three more or less distinct points that are 

 aligned in a sequence of lateral, intermediate, and medial, best seen from 

 the rear. These points correspond fairly closely to the distal ends of the 

 three bones listed and may be called alasphenoid, palatal, and pterygoid 

 points, respectively. In the species inunguis the pterygoid process is 

 long and narrow, and the palatal point is much the highest of the three. 

 In the Congo manatee the pterygoid process is also long and narrow, but 

 here the palatine and pterygoid points are coequal and longer than the 

 alasphenoid. No general rule applies for all specimens of the species 

 manatus that I have examined. In the Florida and Texas specimens 

 that I have seen the pterygoid process is similar to that of the Congo 

 manatee, except that it is usually thicker. In manatees from Guatemala 

 and Puerto Rico, however, the pterygoid process is short and very broad, 

 with either the pterygoid, or palatine point longer. 



According to Hartlaub, the foramen incisivum is always simple in 

 senegalensis, a condition also found in the Congo specimen. The same 

 author observes that this foramen is often completely or incompletely 

 divided in inunguis. The foramen of manatus, however, may not be 

 described as simple, for in a large percentage of the specimens that I 

 have examined there is a partial division into anterior and posterior 

 incisive foramina. Although the division is not complete in any case 

 seen, it is sometimes nearly so. 



The anterior end of the palate of the manatees is covered with a 

 heavy plate that leaves a roughened area on the under side of the pre- 

 maxillae and maxillae. This surface is broadest at about the juncture 

 of the two bones and is constricted just anterior to the level of 

 the foremost teeth. This constriction is most pronounced in inunguis, 

 the width at the constriction being usually about one half that at the 

 maxillary-premaxillary suture. The constriction in manatus and 

 senegalensis, though individually variable, is usually not great, the least 

 width being about 85 per cent of the greatest. 



The molars 1 of senegalensis and manatus seem to me to be indistin- 

 guishable, though they differ strongly from those of inunguis. These 



*At the time the manuscript of this report was in the hands of the printers, I saw in the British 

 Museum a skull of T. manatus (B. M. 370E) from Surinam vvith a left upper incisor in place. This skull 

 had a greatest length of 325 mm., so was adult. The incisor, flattened and almost straight-sided, 

 measured 15.5 mm. in length. Its tip was well worn. There was a single root, but the tooth was per- 

 forated by a foramen from the center of its anterior to the center of its posterior face. 



