﻿28 The Philippine Journal of Science m< 



The subopercles (13) articulate with the opercles (14) dorsally, 

 the angle following the lower margin of the same and over- 

 lapping slightly on the inside. Ventrally and anteriorly they 

 articulate with the interopercles (40), and the anterior dorsal 

 process lies on the inside of the median portion of the preopercles 

 (11). They are lamellar throughout except for a slight per- 

 forated thickening anteriorly and dorsally, and are convex on 

 the outside. The inside of the bone on the left side is shown 

 in Plate VIII, and the outside of the bone on the right side is 

 shown in Plate VII. In Plate VI, fig. 1, the posterolateral 

 margin of the left is seen from the inside. In Plate I the 

 left is shown from without. 



The opercles (14) are roughly right-triangular with the right 

 angle anterior and dorsal, and are convex outwardly. They are 

 thickly lamellar with reinforcements along the anterior margin, 

 dorsoanteriorly, and with a ridge running anteriorly posteriorly 

 about one-third of the distance from the dorsal margin, along 

 the inside. This ridge continues anteriorly in a large expanse, 

 concave anteriorly, which serves for the socket of the posterior 

 end of the head of the hyomandibular (10). The opercles 

 appear to be made up of a considerable number of concentric 

 rings like the shell of the Pelecypoda, with the center, corre- 

 sponding to the umbo of the shell, just inside the socket for the 

 articulation of the posterior end of the head of the hyoman- 

 dibulars (10). The inside of the bone on the left is shown 

 in Plate VIII, and the outside of the bone on the right side 

 is shown in Plate VII. In Plate VI, fig. 1, a part of the inner 

 surface of the left is in view. The left is also seen in Plate I. 



In Plate VIII the left interoperculum (40) is shown from the 

 interior and in Plate VII the right from the exterior. In Plate 

 VI, fig. 1, the inner ventral margin of the left may be seen, 

 and in Plate I the left is viewed. The interopercula overlie the 

 branchiostegal rays (22) and a portion of the epihyals (20), and 

 also posteriorly they overlie the anterior margin of the sub- 

 opercles (13). The dorsoanterior portion lies internally with 

 respect to the ventral part of the preopercles (11), with which 

 they articulate. The dorsal process overlies the epihyals (20). 

 Posteriorly the interopercles are somewhat lamellar, while the 

 anterior portion, as also the dorsal process, is somewhat 

 thickened. Anteriorly they articulate with the posterior portions 

 of the angulars (12) and the articulars (4). 



The mesopterygoids (71) are thin wing-like bones, somewhat 

 convex on the outside, and about twice as long as broad. They 



