712 RHYNCHOPIN^, SKIMMEES. 



in tbe Sterninm generally ; the Bterno-tmclieales join the trachea only three-tenths 

 above the lower larynx. 



Considerable floa'bt has been expressed -whether the Noddies of the siolxdus pattern 

 (excluding those of the blackish tenmi\afris type) are all identical. Jlr. Cai-sin, in 

 lb58, remarks upon certain observable discrepancies; and later I proposed the term 

 frater for the Pacific bird, upon examinaiion of the matter in company with Mr. Cas^siu 

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

 Pacific material in the Smithsonian shows a deeper, though not longer, and cousequeutly 

 differcntly-.sliaped bill ; a diflerent proportion of tarsus to toes ; a much longer toil, 

 with greater emargination and somewhat diflerent coloration. While I would by no 

 means now iusist upon, or even cimcede specific validity in this case, I still think tliere 

 may be a varietal diiference. The case may be sunmied as follows, although there is 

 little or no probability that the name frater is not anticipated. 



Far. STOLiDCS : Wiug, 10 to 10.50 ; tail about 6, the emargination slight ; bill, 0.38 

 deep at base ; tarsns, 1 ; middle toe and claw, 1.45. Occiput bluish-plumbeous, purely 

 -nhiteuing on forehead. Sides of head and neck washed with bluish-plumbeous. Feet 

 drying black. 



Far. FiiATER : Wing, 11 to 11.25 ; tail 7, the emargination 0.50 ; hill, 0.43 deep at 

 base ; tarsus 1 (as in atolidus), 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-s; : Shimmers. 



DiAG. Laridw hypogmailxe, rosiro cultrato, mandiJmld maxilla longiore. 



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

 high and broad. Upper mandible shorter than the under, its cutting edues rapidly 

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

 rami at first widely separated and nearly jiarallel, then rapidly converging to the sym- 

 physis, the union then complete both of tomial and gonydeal margins. Nostri?s basal, 

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

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

 other general characters of Sterninm. 



Upper mandible very freely movable, owing to the mobility of the fronto-maxlllary 

 suture. Mouth short, broad, of moderate gape. Palate flat; internal nares long. 

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

 similar to those of Ster)nii(r. 



The Skimmers are so much the Teras in general character, that no detailed account 

 is required ; but the remarkable peculiarities of the skulls merit special attention. 



Skull. — The most important dift'erences are found in the shape of the cranium ; 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 themselves. 

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

 Laridiiie type, as compared with the special modification of it under consideration. 



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

 cephalic cavitj'. The 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 the 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 hardly ajjpreciable as such ; the dorsum 

 of the occipital hone being very flat, o^ even a little concave. The crotaphyte de- 

 pression between the zygomatic and post-orbital processes is very deep, ftom 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 Puffinus or Golymbus, instead of by a wide space. The anterior division of 

 this temporal fossa (distinctly separated froui the posterior by a well-marked ridge) is 

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



From the narrowness and straightness of the posterior parts of the craniuTn, the 

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

 slightly developed, being iu fact much smaller and uo 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 supra-orbital ridge included between them is not nearly so deeply concave as 

 in the other subfamilies, both on account of the closer approximation of the'post-orhital 



