10 Shufeldt, Osteology of Orthorhamphus magnirostvis. [j^f'""^. 



it is seen to offer a double curve in its entire length. From 

 posterior end to apex, on either side, this curve is upwards, down- 

 wards, and again upwards. The symphysis is extensive, having 

 a length of 2.5 centimeters, being extensively concaved above and 

 correspondingly convex below. Interiorly, the margins are 

 rounded off, and this is true of the osseous tomia above, all to the 

 distal dentary part, where they become sharp. A slit-like vacuity 

 occurs in the splenial space, and a centimeter posterior to it, in 

 either ramus, there is a small, perforating foramen. This foramen 

 is very large and conspicuous in Lams argentatus, but minute in 

 Plovers. 



As already stated, the articular extremities are thick and strong, 

 with their hinder aspects of a triangular outline, the plane of the 

 superficies being at right angles to the long axis of the bone. 



The cranium and this mandible, together with the free associated 

 bones, are nearly entirely pneumatic, and this is generally the 

 case in the other forms here mentioned. 



In the Chilean Lapwing [Belonopterns) the mandible possesses 

 well-developed angular processes posteriorly, and this is the case, 

 too, in Squatarola : while in most Gulls the mandible is very much 

 like that bone in Orthoyhamphus. In fact, this jaw would answer 

 pretty well for some of the larger species of longipennine birds. 



The Hyoid. — In this, the skeletal part of the lingual apparatus, 

 we find extreme simphcity of structure. The anterior cartilaginous 

 extension of the glosso-hyal is long (2.5 cms.) and narrow (average 

 1.5 mm.), terminating in front as a rather pointed tip. Basally 

 it ossifies to a certain extent, forming a bone some 4 mm. long, 

 and just large enough to accommodate the articulation for the 

 basi-hyal. This latter is of quadrilateral outline, with the usual 

 anterior, median process for the glosso-hyal. consisting of a short 

 superior lip and a long inferior one. Posteriorly, its margin is 

 transverse, and occupied by a median facet for the free uro-hyal 

 or hasi-hranchial. On either side of this is the facet for the 

 cerato-hranchial of the thyro-hyals for the corresponding side. 



Either epi-hranchial ossifies all to a small part of its hinder end, 

 and the cerato-branchial and epi-branchial taken together exhibit 

 a considerable curvature, the first-named having a length of 

 3.2 cms. and the latter 2 cms., not including its cartilaginous part. 

 (Plate II., fig.' 2.) 



In Squatarola squatarola no part of the glosso-hyal ossifies ; the 

 basi-hyal is narrow and elongate, and the uro-hyal co-ossifies with 

 it. The thyro-hyals are extremely slender and long, agreeing, 

 apart from their smaller size, with those elements of the hyoid 

 in Orthorhamphus. 



Rissa tridactyla (No. i8,i6q. Coll. U.S. Nat. Mus.) exhibits con- 

 siderable difference in its hyoid. as compared with the limicoline 

 species just noticed. In this Gull a large part of the glosso-hyal 

 ossifies — that is. some 1.3 cms. of its posterior portion, and only 

 about 8 mm. of its anterior tip remains in cartilage in the adult. 

 The ossified part is elongate and narrow (V-shaped), being com- 

 posed of two small rods of bone placed side by side and bridged 



