REPORT ON THE ANATOMY OF THE PETRELS. 



47 



developed transverse processes, and between their centres inferiorly small chevron bones, 

 smallest anteriorly, larger and double posteriorly, are developed. The last of these 

 may, apparently, anchylose with the body of the corresponding vertebra. The pygostyle 

 is long and compressed. The diving Pelecanoides has, it will be noticed, a greater number 

 of vertebrae (9) in its tail than the other forms. 



Table showing the Numbers of the Vertebr.e, Ribs, and Uncinate Processes. 



Pectoral arch. — The sternum (PL VII.) is usually rather broad and short, much longer 

 in Pelecanoides than in any other genus, with a well- developed keel, and a short, but dis- 

 tinct manubrium — obsolete in Pelecanoides. The costal processes are triangular in shape, 

 directed outwards, or in the Oceanitidse and Pelecanoides, forwards and outwards. The 

 anterior margin of the keel is more or less excavated, with its lower angle produced 

 forwards, most so in Puffinus anglorum. In Pelecanoides (PI. VII. figs. 3, 4) this part 

 articulates with the clavicular symphysis, instead of being merely connected to it by 

 ligament, as in the other forms. The coracoidal grooves are oblique backwards, and 

 present two distinct articular areas for the articulation of the coracoid bone. The sides 

 of the sternum usually converge towards the lower end of the costal process, and then 

 diverge again to their posterior extremities. As may be seen from the figures of Piatt' VII. 



