OSTEOLOGY OF LARID^. 



595 



the tip, where it is considerably decnrved, in Lams and Stercorariiis ; in Sterna no such 

 deflection exists. The articulating surface has, as usual, an internal deep concavity, 

 and au external more shallow portion, both being bounded posteriorly by a raised 

 border. The internal process of the articulating surface is well developed and rather 

 acute ; and from the external edges of the articulation there proceeds downward and 

 forward on the edge of the jaw a raised line, for muscular attachments, most conspicu- 

 ous in Larus. The surface of bone just posterior to the articulation, for the attachment 

 of the digastricus, is of a triangular shape, and its face presents backward and down- 

 ward instead of backward and upward, as in some other natatorial genera. 



The tomial edges of the inferior maxilla are thin, sharp, and erect ; while tho.se of 

 the mandibular processes of the intermaxillary are broad and ilat, without sharp edges. 



* Inches and hundredths. 



+ The greatest depth in Larinm, Lestridinw, and Sierninw is opposite the coronoid pro- 

 cess. In BhynchopincB the depth just anterior to the symphysis exceeds this, the depth 

 at the coronoid process being only 0.45. 



SpiNAi COLUMN. — The number of vertebrse throughout the four subfamilies is nearly 

 constant, varying at most by one or two vertebrai, if at all. The Sterninw appear to 

 have one less vertebra in the sacrum, i.e., eleven instead of twelve ; but this is the 

 only difference that I have been able to discover. The following table exhibits the num- 

 ber of vertebrae belonging to the different spinal regions in three of the four groups : 



Species. 



O 



Stercorarius pomatorhinus 



Larus argentatus 



Sterna hirundo 



