NATURAL SCIENCES OF PHILADELPHIA. 215 



a scattering group. And in general among birds, the closer the inter rela- 

 tion of forms included in a group of any grade, the more definitely circum- 

 scribed is that group from its surroundings ; and conversely. 



Fam. ScuD.E. — Bill very short, serrate, decurved at tip, but not hooked 

 with a distinct nail ; its covering continuous. Nostrils abortive. Gular sac 

 undeveloped. Wings mediocre. Tail large, cuneate, definitely few (12 — 14)- 

 feathered. Head not crested. Feet ambulatorial. Body with remarkable 

 pneumaticity ; not much depressed. Taken from* Geese. Technically one 

 sub-family. Genus : Sula ; perhaps another sufficiently distinct. 



Evidently anserine in form and general appearance, as well as many details.^ 

 The serrated simulates the lamellaied bill. The wings are like a goose's ; 

 the tail of few leathers repeats that of some Anatidse ; the feet are strongly 

 ambulatorial. 



Fam. Pelecanidje. — Bill very long, slender, but strong; its covering not 

 continuous ; not serrate ; distinctly hooked with a nail. Nostrils rudimentary. 

 Gular sac at a maximum. Wings extremely long, with upwards of forty 

 remiges. Tail short, rounded, indefinitely many-feathered. Head crested. 

 Legs columnar, very stout. Body with unusual pneumaticity: moderately 

 depressed. Taken from Albatrosses. Technically one subfamily. Genus : 

 Pelecanns ; perhaps another. 



The immense, many-feathered wings, and the size and general appearance 

 of these birds, recall the Albatrosses. So does the hamulate, broken-covered, 

 non-serrate bill. Progression in either of the three elements is similar ; neither 

 of the birds can swim under water. The enormous pouch represents the ex- 

 treme of development in the order. Yet some of the family to which Alba- 

 trosses belong have it; witness the genus Pelecaiioides. 



Fam. PHALACROCORACiD.?i. — Bill mediocre in length, rather slender, strongly 

 hamulate, non-serrate, but its covering scarcely broken. Nostrils obliterated, 

 at least in the adult state. Gular sac moderate. Wings short or medium. 

 Tail large, fan-shaped, very stiff, definitely few (12 — 14) feathered. Head 

 with curiously modified feathers. Legs far back, not ambulatorial : upright 

 position necessitated. Pneumaticity slight. Body greatly depressed. Heavy 

 flyers; excellent divers. Taken from Auks. Technically one subfamily. 

 Genus: I'halacrocorax ; but probably capable of well-founded divisions. 



These are palpably pygopodous ; representing the extreme, in this respect, 

 of the present order. They are forced to stand upright, and use the tail as 

 additional support. They progress under water better than any other toti- 

 palniate birds, except the Ploiidce. The curious colored feathers about the 

 head are those of Auks and Penguins. By remote analogy, there is a resem- 

 blance to Scansores. 



Fam. Plotid^e. — Bill very slender, straight, not hooked, sharply paragna- 

 thous, subserrate, its covering continuous.. Nostrils minute. Gular sac 

 small. Wing short. Tail large, fan-shaped, 12-feathered. Legs far back ; 

 used on land chiefly in perching ; position more or less upright. Pneumaticity 

 ordinary. Body depressed. Poor flyers; unsurpassed divers. Taken from 

 Grebes. Technically one subfamily. Genus: Plotus. 



The analogy, if not actual affinity, is very striking in this case. Physic- 

 ally, the long neck, style of bill, shape of wings and position of feet, are like 

 the same parts in PodidpidcR. Physiologically the Darters share with the 

 Grebes a habit almost confined to these two families: that of sinking back 

 quietly in the water, leaving only the ^bill exposed. Both are unrivalled 

 divers. Moreover, we have in that singular family, the HeliornitJiidce^ an 

 actual link between Grebes and Darters ; further carried to falicarious 

 forms. 



* Not actually, of course, but potentially, or ideally. 



1869.] 



