NO. II CLASSIFICATION, BIRDS OF THE WORLD — WETMORE 7 



included in the Hydrobatidae have a simplified condition in the 

 quadrato-tympanic region of the skull in which the opening of the 

 upper tympanic recess is small, and is so located that it separates the 

 squamosal and opisthotic facets. In addition, the posterior border of 

 the sternum is truncated and entire, and basipterygoids are absent or 

 are represented only by small spines. In the Procellariidae, on the 

 other hand, the foramen of the upper tympanic recess is greatly 

 enlarged and lies anterior to the two facets for the quadrate, which 

 are joined by a bridge of bone; the posterior border of the sternum 

 is notched ; and basipterygoid processes are present. These constitute 

 distinctive characters at the family level. 



The Pelecaniformcs. — In the arrangement of suborders in the order 

 Pelecani formes we encounter in marked degree the standard difficulty 

 of logical placement in linear alignment of groups that really stand in 

 three-dimensional relationship. Lanham (1947, pp. 65-70) has made 

 a summary of the major anatomical characters of the group in which 

 he points out the differences that set off the Phaethontes and the 

 Fregatae from the Pelecani. There is no question that the first two 

 carry primitive characters, which may be presumed to be similar to 

 those found in ancient ancestral stocks, since in these resemblances 

 they are more like other types of birds, notably the Procellarii formes. 

 From this style the families of the suborder Pelecani have become 

 widely divergent. Although the tropicbirds and the frigate-birds both 

 have retained a part of what may be regarded as a basic pattern, they 

 are so distinct in other respects that it appears to be more reasonable 

 to relate them individually as branches from a common stock rather 

 than to combine the two on one line, separate from the Pelecani. The 

 Phaethontes possibly may have separated earlier than the Fregatae. 

 Among interesting differences other than those of internal anatomy, 

 it may be noted that the tropicbirds have the young covered with down 

 at birth and that the adults possess series of air cells under the skin on 

 the forepart of the body like those found in pelicans and boobies. The 

 frigate-birds have young almost naked at hatching, and the emphy- 

 sematous condition is mainly lacking. In view of this I prefer to 

 continue to align these groups on either side of the Pelecani. 



Though there is no question that the cormorants and snake-birds 

 are closely allied, they differ in such degree that they should be retained 

 in separate family status. The snake-birds are marked by a peculiar 

 conformation of the cervical vertebrae through which the beak be- 

 comes a triggered spear in feeding. The bridge of Donitz on the ninth 

 vertebra is an important part of this arrangement. The stomach also is 

 unusual in possessing a curious pyloric lobe, lined with a mat of hair- 



