204 PROCEEDINGS OF THE ACADEMY OP 



tic of the longest-winged and best flying family (Frocellariidse) of swimmers. 

 Among higher birds it again occurs in certain Strisorcs, especially Caprimul- 

 ffidcc, as well seen in Siphonorhis. It is interesting to observe that these birds, 

 like the petrels, are among the longest winged and best flying of their own 

 sub-class. And further, that they mock the swimmers in the elevation 

 and sometimes lateral position of the hind toe, together with the presence 

 of a membrane between the toes not to be distinguished from a true " web," 

 and equal in amount to that of many " semipalmate" waders. This is entirely 

 dift'erent from the actual cohesion of the toes that obtains in many Insessores. 

 The obliquity of the hind toe, too, is the necessary antecedent feature to its 

 union by webbing with the second toe, as in all steganopods. Pectination of 

 the middle toe is another feature of these long winged Strisores, repeated in 

 the lougest winged swimmer — Tachypetes. Finally, the characteristic gular 

 pouch of all totipalmates is represented virtually, if not actually, in the 

 broad-mouthed, loose-throated Goatsuckers, &c. 



The scapsorial type is exemplified in certain swimmers. One of its essen- 

 tial features is such construction of the tail as will allow of this being used 

 as an additional means of support, as best illustrated in the woodpeckers. 

 It is repeated in the cormorants ; birds with long, strong, stiff tail feathers, 

 that use the tail as a third-base of support when standing on level ground, 

 and exactly as woodpeckers do, when clinging to rocky ledges. Phalacro- 

 coracidx a.ve scansorial Naiatores. 



A certain family of higher " land"-birds is purely aquatic, deriving its whole 

 subsistance from the water. I refer to the kingfishers. Their characteristic 

 habit of sitting on projecting branches watching for their prey, and darting 

 into the water to secure it, are repeated in the Flotidie. In both families 

 progression on land is almost denied. 



The term " sea-swallow," universally applied in our own and other lan- 

 guages ("Hirondelle-de-mer," " Meerschwalbe,"&c.) to the Stcrninx, is expres- 

 sive of a strong analogy, traceable both in general conditions and special 

 characters. As to the former, I need only refer to mode of flight, and man- 

 ner of hunting for prey, especially in such small delicate species as Hydro- 

 clielidonfissipes, e. g. The " skimming" of the swallow in the air, and its atti- 

 tudes on the ground, are repeated in the tern. As to special physical points, 

 I may instance shape of wing, and relative length of that member ; length 

 and furcation of the tail; and the remarkable shortness of the legs that in 

 both groups readers walking difficult and unusual. 



In the active pursuit of prey under water, the very highest Oscines are 

 brought into analogical resemblance with the lowest swimmers, by the sin- 

 gular genus Cinclus. 



I do not observe any special analogies of anatiform swimmers with higher 

 birds; though some might possibly be traced. This strictly monomorphic 

 family seems specially reserved as the means of perfect transit from swim- 

 mers to waders through PhoRnicopterus. 



Characters of the sub-class. 

 No one character can define Nntatores. Covering of the knee by the skin 

 of the body is the most general one, and one probably not found outsidethe 

 sub-class ; but it varies down to a minimum, ceasing to be diagnostic in cer- 

 tain Longipcnnes. Web-footedness is not an infallible indication ; some 

 Grallx are palmiped, some Naiatores are not. But these two, with qualified 

 reference to two others, furnish the desired definition. Thus Xatatores are 

 palmiped with the knee internal ; or, if external, the bill neither recurved nor 

 abruptly decurved ; or lobiped, with the tail rudimentary.* 



* It might be advanced here, that I am liable to the charge of doing what I have above 

 criticized others for doing, i. e.., making a division upon a single feature. But there is a 

 distinction between simple "detinition" (». e. limiting) of a group, and its "characteriza- 

 tion" in full. The foregoing phrase is merely a convenient word-formula for the ready 

 recognition of any Natatorial bird, which could only be " characterized " by reference to 

 several other features. 



[Dec. 



