NATURAL SCIENCES OF PHILADELPHIA. 218 



A fourth group is represented bj' three genera, JEstrelata., Fagodrorna and 

 Daplion, each distinctly characterized. The two last are unispecific. In the 

 first I throw the very many species agreeing in medium size, strong largely- 

 hooked bill, long wedge-shaped tail, and rather short wings. Its species have 

 received a dozen, more or less, generic names. There are about a score of 

 them. Daption is peculiar in its wide bill, with rudimentary lamella' and 

 quasi-gular pouch, indicating Auseres and Steganopods. Payodroma is among 

 petrels much what Gggis is among terns, and Pagophila among gulls. 



The last group, called Prionem, is remarkably distinguished by the lamina- 

 tion of the bill, equal, in one genus, to that of Lamellirostres, and only here 

 found outside that order. There is also a shape of bill in Prion corresponding 

 to Cancroma among Herons ! and the throat is somewhat pouched. One square- 

 tailed, light-colored form llalohwna recalls the Gulls. Genera : Ilulobxna, 

 Pseudoprion Prion. 



Subfam. Halodrominx. — Nostrils superior, vertical, united, on the culmen at 

 base. Mandibular sj^ace wide, with a distensible skin. Feet tridactyle. Wings 

 and tail, and general form, of AlcidcE ! Genus: Pelecanoides (Lacep., about 

 1800 ; = Halodroma, 111. 1811, et auctt ) 



A singularly aberrant form, only Procellaridian in the uostrils ; standing at 

 a point where Lonffipeiuie.s, Steffanopodes and Pi/yopodes meet; Steganopodous in 

 its dilatable throat, &c. ; Pygipodous in feet, wings aud tail. It is almost a 

 3fer(/idus. 



Fam. Larid.*:. — Bill generally with continuous covering. Nostrils always 

 lateral, linear, or lance-linear. Wings always long and pointed, reaching far 

 beyond base of tail. Tail alwa3-s well developed, definitely few-feathered (12 

 rect.), but of varying shape. Feet always tetradactyle ; hallux small, simple, 

 elevated, apparently never functional. Strong dashing flyers, good light 

 swimmers, poor divers. Altrices. 



A definitel}' circumscribed gronp, without any remarkably' aberrant forms. 

 Sharply divided bj' characters of bill, &c., into four subfamilies, thus :— 



Subfam. Lestridince — Covering of bill not continuous ; upper mandible in- 

 structed with a distinct cere; bill epignathous.* Tail squarish, but median 

 rectrices abruptlj^ long-exserted. Head never crested. Tarsi rugose ; feet 

 arabulatorial. Genera: Biiphaffus,f Stercorarius.f 



Comprehending the " Jaegers," or "Skua Gulls." Affording the only in- 

 stances in the subclass of a cered bill. In this partition of the rostral envelope 

 we have an interesting approach to an essential character of the preceding 

 family, — an affinity borne out by the pterylosis. For, says Nitzsch, in the 

 Proceilariidse " the tract formation of Leatris is elevated into the type of a 

 group '■ The peculiar construction of the tail is only elsewhere met with 

 among water birds in the Anserine genus Harelda and the Steganopodous one 

 Phaethon. The Jaegers are marine Accipitres ! 



* There are only four possible conditions of the bill, with reference to the relaticm of the 

 tips of the mandibles to each other. (1) the upper mandible overreaches the under, and 

 is deflected over it; (2) the under mandible extends beyond the upper; (3) the two meet 

 at a point; (4) the points of the mandibles cross each other. I propose to call these con- 

 ditions rpif/nathous, hypofjnathnus. piiragtiathnns and mHagnathous respectively. Tlie first is, 

 exemplified by all the Raptomx, J'.-iittaci, ProceMariidse. &c., &c. The second is exemplified 

 by the Bhynchopinte. The majority of birds, especially Passeres, exhibit the third. Of 

 the fourth I only Ivnow one instaace, — the Cross-bills (C(o-(u')-o.5<ra .Scop. = ioxm auctt.1 

 The family Laridse is the only one that comprehends examples of three of these forms ; 

 and here they are, as we have seen, almost diagnostic of the subfamilies. 



In respect of the epignathous type, it should be noted that to constitute this form thf 

 modification should affect the premaxillary ilself, and be perceptible in the skeleton ; 

 mere ileflection of a point or margin of the corneous envelope of the bill is not sufficient; 

 e. fif., Empidonace.s are paragnathous. 



That singular bird, the il«aW/.i/nc/i2<.'t. might be thought to repres^ent a fifth kind ; V>ut I 

 should judge it to be paragnathous. The modification in this case is of a different kind 

 altogether; a species of bilateral asymmetry, like the bent vomer of certain cetaceans. 



fif Mcehring's and Brisson's genera camnot obtain, we must take Cu^/iaracto, Brunn„type 

 C. skua, Brtinn., and Lestris, 111., type L. parasitica, Linn. 



1869.] 



