BIRDS OF NORTH AND MIDDLE AMERICA. 449 



Characters possessed in common by the Lari and the Limicolse, as 

 opposed to the Alcae, are given on pages 2 and 3. Those possessed by 

 both the Lari and the Alcse but not shared by the Limicolae are as 

 follows : 



Hypotarsus simple (without canals); supraorbital grooves large; 

 bill and legs relatively short and stout; anterior toes fully webbed 

 (with a few exceptions) ; young tardily nidifugous (nearly nidicolous) ; 

 habits aquatic. 



The Lari are long-winged swimming birds, of graceful, bou3"ant, 

 and powerful llight, with anterior toes more or less fully webbed, the 

 hallux small and elevated, sometimes rudimentary or nearly obsolete, 

 and the legs are attached near the middle of the body, which therefore 

 assumes a nearly horizontal position when the birds are standing or 

 perching. Their nidification is not materially different from that of 

 the Limicolffi, but the young remain longer in the nest than those of 

 the latter group, being, in fact, more nidicolous than nidifugous. 



Distribution, cosmopohtiin. 



KEY TO TUE FAMILIES OP LARI. 



a. Ambiens muscle and biceps slip absent; tendons to ulna side of arm, 2; bill pecu- 

 liar, the mandible much longer than the maxilla, both excessively compressed. 



Rynchopidae (p. 449). 

 aa. Ambiens muscle and biceps slip present; tendons to ulna side of arm, 1 or none; 

 bill not peculiar. 

 b. Ramphotheca simple (bill without cere); caeca rudimentary (except in genus 

 Gygis of Sternidse); metastermum 4-notched; coracoids in contact; claws mod- 

 erately to feebly developed, 

 c. Thigh-muscle formula with B (except in Gygis); expansor secundariorum absent 

 (except in Anous); exposed culmen at least one and one-fourth (sometimes 

 nearly three times) as long as tarsus, the latter usually less than one-tenth 

 (never much more than one-ninth) as long as wing; tail usually (often 



deeply) forked; pterylosis typically charadriine Sternidae (p. 458.) 



cc. Thigh-muscle formula without B; expansor secxuidariorum present; exposed 

 culmen less than one and one-fourth times as long as tarsus (usually shorter 

 than tarsus), the latter more than one-tenth (sometimes more than one-sixth) 

 as long as wing; tail usually truncate or slightly rounded, rarely graduated, 

 never very deeply forked; pterylosis not typically charadriine. 



Laridae (p. 561). 

 bb. Ilhamphotheca complex (bill with a cere); caeca well-developed, long; cora- 

 coids separated; metasternum 2-notched; claws large, strongly hooked, 

 sharp Stercorariidae (p. G76). 



Family- RYNCHOPID^. 



THE SKIMMERS. 



— Rhyyichopsina: Boxaparte, Geog. a«id Comp. List Birds, 1838, 60. 



=Rhynchopinse Lawrence, in Baird, Rep. Pacific R. R. Surv., ix, 1858, 837, 865. — 

 Carus, Ilandb. Zool., i, 1868, 362.— Coues, Proc. Ac. Nat. Sci. Phila., 1869, 

 314; Key N. Am. Birds, 1872, 323; 2d ed., 1884, 734, 772; Bii-ds Northwest, 

 1874, 712. — ScLATER and Salvin, Nom. Av. Neotr., 1873, 147. — Stejneger, 

 Standard Nat. Hist., iv, 1885. 83, in text.^GAOow, in Bronn's Thier Reich, 



40017— 19— Bull. 50, pt 8 30 



