700 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
Suborder ALC. 
THE AUK TRIBE. 
>Pygopodes ScuateR, Ibis, 1880, 409 (includes Gaviidz).—AMERICAN ORNITHOL- 
ocists’ Union, Check List, 3rd ed., 1910, 21 (Alce+Gaviide-+Colym- 
bide). 
Satie SresneceR, Standard Nat. Hist., iv, 1885, 68, in text (includes 
Gaviide). 
=Aleex Suarrz, Review Rec. Att. Classif. Birds, 1891, 72.—GRANT, Cat. Birds 
Brit. Mus., xxvi, 1898, xvii, 559.—Bepparp, Struct. and Classif. Birds, 1898, 
359.—SaLvin and Gopman, Biol. Centr.-Am., Aves, iii, 1904, 446.—OxEr- 
HOLSER, Outl. Classif. N. Am. Birds, 1905, 3. 
= Alciformes Suanre, Review Rec. Att. Classif. Birds, 1891, 72; Hand-list, i, 1899, 
xiv, 130. 
>Cepphi American OrnitHozocists’ Union, Check List, 3rd ed., 1910, 24 (in- 
clude Gaviide). q 
Short-winged, pygopode, aquatic (natatorial) Charadriiformes 
with space between supraorbital grooves compressed into a ridge; 
basipterygoid processes absent in adults; occipital fontanelles pres- 
ent; hemapophyses of dorsal vertebre large and conspicuous; ster- 
num long and narrow, the metasternum rounded posteriorly and 
longer than the postero-lateral processes; thigh-muscle formula with- 
out Y, usually without B; tensores patagii and biceps slip.peculiar; 
hallux always absent, and anterior toes always fully webbed. 
Basipterygoid processes absent in adults, vestigial and fused with 
nasals in young; temporal fosse 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; vertebre all free; cervical vertebre, 
15; anterior dorsal vertebre with very conspicuous hemapophyses, 
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 
