Vol. xv.n 5hufki.I)T, Osteology oj Oyl/iorhamphus magniroslris. 13 



to the very slender second pair of sacrals do not reacli, on either 

 side, the sternum, by at least a centimeter or more. (Fig. 8.) 



'I'lic Sternum (fig. 8, Plate IV. ; fig. 10, Plate V.)— In this bone 

 \vc have an interesting combination of characters ; and, while 

 these are largely ))luviahne, there is yet to be* seen evident traces 

 of larine ones. Quadrilateral in general outline, the bone has 

 an extreme length of 8|- cms., and an average width of 3I cms. 

 An imaginary line, measured from the postero-superior angle of 

 the small, sessile, quadrilateral manubrium to the angle of the 

 deep and anterior i)rojecting carina, measures 3.3 cms., while 

 the keel itself has an extreme length of 9.1 cms. 



Dorsally, this sternum is markedly concaved, and does not 

 appear to be pneumatic, as the foramen just within the thickened 

 anterior border, mesially, is absent. There is a large, elliptical 

 one present in Larus argentatus. and a small one in the sternum 

 of a Kittiwake (Rissa). 



The sterna of Cliionaychus. most Plovers, Oyster-catchers, and 

 Turnstones and their allies are non-pneumatic, and the aforesaid 

 foramen is absent. 



Orthorhamphns has the costal processes of its sternum large 

 and almost square in outline, the posterior border of either one of 

 them affording space for well-separated transverse facets for the 

 three leading costal ribs or haemapophyses. The manubrium 

 stands squarely between the transversely long coracoidal grooves, 

 and the sharp mesial anterior edge of the former is carried half- 

 way down to the carinal angle, the anterior border of the keel 

 being much thickened here, while for the rest of the distance to 

 the angle it is thin and sharp. 



Passing to the posterior part of the body of the sternum (figs. 8 

 and 10), we find a long, very slender, external xiphoidal process 

 on either side, which very nearly surrounds a large, elliptical 

 xiphoidal opening. These lateral processes nearly close in, on 

 either side, the opening posteriorly. Mesially, the midxiphoidal 

 prolongation is transv^ersely broad, terminating posteriorly in a 

 transverse border. On the left-hand side of the keel this pro- 

 longation is pierced by two foramina — one small, antero-external 

 circular one, and one, rather large, postero-external elhptical one. 

 On the right-hand side there are two more — a very small, antero- 

 external circular one, and a much larger circular one, situated 

 at a little distance posterior to it. 



As a rule. Plovers have their sterna profoundly twice-notched 

 on either side of the sternal keel [Squatarola, Charadriits, Lobi- 

 vanelliis, &c.) ; this is also the case with Hcematopus. 



Belonopterus chilciisis has large, external " notches " and much 

 smaller internal foramina, this being reversed in Larus argentatus. 

 Chionarchus minor agrees, in this particular, with Rissa tridadyla 

 and probably with other Gulls, all of which proves that we must 

 be quite cautious when we come to employ the morphology of 

 the xiphoidal extremity of the sternum of birds as the sole 

 character in tracing affinities in this group. 



