OSTEOLOGY OF LARIDJE. 



595 



the tip, where it is considerably decnrvcd, in Larus and Stercorarius ; in Sterna no such 

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

 and an 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 aud 

 forward on the edge of the jaw a raised line, for muscular attachmeots, 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 thiu, sharp, and erect ; while those of 

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



$ Table shoiving the comparative proportions, and relative si:es of the skulls of the four sub- 

 families of Laridw. 



* Inches and hundredths. 



t The greatest depth in Lariiue, Lestridinai, and Sternina; is opposite the coronoid pro- 

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

 at the coronoid process being only 0.45. 



Spinal column. — The number of vertebra) throughout the four subfamilies is nearly 

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

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

 only dilferencc that I have been able to discover. The following table exhibits tlie num- 

 ber of vertebraj belonging to the difl'erent spinal regiotis in three of the four groups: 



Species. 



Stercorarius pomatorhinus. 



Larus argcntatus 



Sterna hirnndo 



C5 

 « 



a 



CO 



1'^ 



I o 

 O 



12 8 



8 

 11 i 8 



o 



42 

 42 

 41 



