r^ 



712 RHYNCHOPIN^, SKIMMERS. 



in the Sternhuv generally; the steruo-traclieales join the trachea only three-tenths 

 above the lower laiyiix. 



Coiisideralile doubt has been expressed whether the Noddies of the sfolidtis jiatterii 

 (excluding those of the bhiekish teiiuir^slris type) are all identical. Mr. Cassin, in 

 1^58, remarks npon certain observable discrepancies; and later I propo.sed the term 

 frater lor the Paeiiie bird, npon examinafion of the matter in company with Mr. Cassin 

 and Prof, liaird, who both agreed that there were recognizable peculiarities. The 

 Pacilic niateiial in the Smithsonian shows a deeper, though not longer, and conseqnently 

 diilercnily-shaped bill; a diflerent pro])ortion of tarsus to toes; a mnch longer tail, 

 with gieater eniargiuation and somewhat diflerent coloration. While I would by no 

 means now insist npon, or even concede specific validity in this case, I still tliink tLere 

 may be a varietal difference. The case may be snmnied as follows, although there is 

 little or no ])robability that the name frater is not anticipated. 



Var. STOLiDUS : Wing, lU to 10.50; tail about fi, the emargination slight; bill, 0.38 

 deep at base ; tarsus, 1 ; middle toe and claw, 1.4.5. Occipnt Iduish-plumljeous, purely 

 whitening on forehead. Sides of head and neck washed with blnish-i)lumbcous. Feet 

 drying black. 



Frtr. fkater: Wing, 11 to 11.25; tail 7, the emargination 0.50; bill, 0.43 deep at 

 base ; tarsus 1 (as in stolidus), but middle toe and claw 1.60. Occiput brownish-ash, 

 becoming ashy-white on the forehead. Sides of head and neck like rest of body. Feet 

 drying reddish-brown. 



Subfamily Ehynchopin^ : SMmmers. 



DiAG. Laridci InjjjogvuiJia:, rosiro cultruto, mandihald max'iUd longiore. 



Body slender and elongate. Neck of moderate length. Head large ; the forehead 

 high and broad. Upper maudible shorter than the under, its cutting edges rapidly 

 converging to the nostrils, thence parallel and closely soldered to the tip. Mandibular 

 rami ;it iirst widely separated and nearly parallel, then rapidly converging to the sym- 

 physis, the nniou then complete both of toniial and gonydeal margins. Nostrils basal, 

 inferior, their near end behind the projection of the feathers on the culmeu. luterra- 

 mal space fully feathered. Tibise anteriorly scutellate. Remiges, 10 ; rectrices, 12 ; and 

 other general characters of Stermna. 



Upper maudible very freely movable, owing to the mobility of the frohto-maxillary 

 suture. Month short, broad, of moderate gape. Palate tlat ; internal nares long. 

 Tongue short, broad, fixed. Digestive and respiratory organs, in all essential respects, 

 similar to those of Sternhuv. 



The Skimmers are so nnich the Terns in general character, that no detailed account 

 is re(|uired ; but the remarkable peculiarities of the skulls merit special attention. 



Skull. — The most important ditferences are found in the shape of the craniuin ; in the 

 fronto-maxillary suture, and other elements which enter into and produce the mobility 

 of the superior mandible : and in the shape and character of the mandibles tliemsel ves. 

 In the terms used in the following description, reference is always had to the normal 

 LaruVnie type, as compared with the special moditicatiou of it under consideration. 



The cranium is exceedingly narrow posteriorly, at that portion which forms the en- 

 cephalic cavity. Tbe post-orbital are hardly, if at all, more widely separated than are 

 the ante-orbital. The convexity of the vertex of the cranium antero-postei iorly is very 

 slight indeed, and tbe superior curved line of the occiput rises high up and is exceed- 

 ingly prominent. Its inferior extremities curve greatly forward and outward, forming 

 very protuberent zygomatic processes overhanging the articulation of the tympanic 

 bone. At the same time the occipital ridge is hardl}'^ a^jpreeiable as such ; the dorsum 

 of the occipital bone being very ilat, o'' even a little concave. The crotaphyte de- 

 pression between the zygomatic and post-orbital processes is very deei>, from the great 

 bulk of the muscles lodged in it. This increased volume of muscle is also indicated by 

 the meeting on the median line of the skull of the two roughened depressions which 

 lodge the temporalis, these depressions being only separated by a narrow longitudinal 

 ridge, as in Fiiffinus or Cnhimhits, instead of by a wide space. Tiie anterior division of 

 this temporal iossa (distinctly separated from the; posterior by a Avell-marked ridge) is 

 also deeiJ, and extends further toward the median line of the skull. 



From the narrowness and straightuess of the posterior parts of the cranium, the 

 orbits are notably wide and shallow. Their posterior processes are very small and 

 slightly developed, being in fsict mnch smaller and no more widely separated from each 

 other than the anterior processes. These latter are remarkably developed, being 

 large, broad and heavy, and projecting backward and outward with very convex out- 

 lines. The suj)ra-or1)ital ridge included between them is not nearly so deejily concave as 

 in the other subfamilies, both on account of the closer ai^proximation of the post-orbital 



