700 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



Suborder ALC^. 



THE AUK TRIBE. 



'^Pygopodes Sclater, Ibip, 18S0, 409 (includes Gaviidse). ^-American Ornithol- 

 ogists' Union, Check List, 3rd ed., 19]0, 21 (Alcse+Gaviidae+Colym- 

 bidte). 



"^Alcoidese Stejneger, Standard Nat. Hist., iv, 1885, 08, in text (includes 

 Gaviidse). 



=Alcx Sharfe, Review Rec. Att. Classif. Birds, 1891, 72.— Grant, Cat. Birds 

 Brit. Mus., xxvi, 1898, xvii, 559! — Beddard, Struct, and Classif. Birds, 1898, 

 359. — Salvin and Godman, Biol. Centr.-Am., Aves, iii, 1904, 446. — OsfiR- 

 HOLSER, Outl. Classif. N. Am. Birds, 1905, 3. 



=Alciformes Sharpe, Review Rec. Att. Classif. Birds, 1891, 72; Hand-list, i, 1899, 

 xiv, 130. 



"^CeppM American Ornithologists' Union, Check List, 3rd ed., 1910,24 (in- 

 clude Gaviidfe). 



Short-winged, pygopode, aquatic (natatorial) Charadriiformes 

 with space between supraorbital grooves compressed into a ridge; 

 basipterygoid processes absent in adults; occipital fontanelles pres- 

 ent; haemapophyses of dorsal vertebree large and conspicuous; ster- 

 num long and narrow, the metasternum rounded posteriorly and 

 longer than the postero-lateral processes ; tliigh-muscle formula with- 

 out Y, usually without B; tensores patagii and biceps slip pecuhar; 

 hallux always absent, and anterior toes always fully webbed. 



Basipterygoid processes absent in adults, vestigial and fused with 

 nasals in young; temporal fossae deep; supraorbital grooves deep, 

 meeting along median line (the space between them compressed into 

 a ridge); interorbital septum very incomplete; occipital fontanelles 

 present, well-marked; a well-developed "cerebellar dome;" vomer 

 free, blade-like, cleft posteriorly; maxillo-palatines laminate; lachry- 

 mals firmly united with prefrontals; dentary suture of mandible 

 with a well-defined lower limb ; vertebrae all free; cervical vertebrae, 

 15; anterior dorsal vertebrae with very conspicuous haemapophyses, 

 bifid at their free ends; neural spines and transverse processes with 

 long tendinous ossifications; corpus sterni greatly elongated, the mata- 

 sternum rounded posteriorly, 2-notched, 1-notched (medially), or 

 entire, projecting beyond postero-lateral processes; a spina communis 

 between coracoid grooves; coracoids without a subclavicular process, 

 the ectepicondylar process minute or absent; furcula with a facet for 

 articulation with acrocoracoid, and connected with the latter only; 

 pelvis laterally compressed, the pre-ilium longer than post-ilium, the 

 two separated from one another by dorsal border of neural spines of 

 synsacrum; post-ilia with a more or less extensive flattened dorsal 

 surface, and separated from one another by transverse processes of 

 synsacrum; pubes of great length (as long as or longer than whole 

 ilium); ribs attached to sternum, 7; posterior dorsal and ventral 

 ribs of equal length, running backward as far as free ends of pubes; 

 cnemial crest not greatly produced beyond level of articular surface 



