16 PROF. T. JEFFERY PARKEH ON THE 



The opercular {op) is a large flat bone articulating by a well-marked concave facet 

 with the opercular process of the hyomandibular (fig. op^). In the neighbourhood of 

 this facet it is of tolerable thickness, but in the rest of its extent it is extremely thin, 

 and cracks readily at the edge on drying. Its dorsal edge is maiked with three strong 

 crenations, its posterior border is gently sinuous, its antero-ventral border evenly 

 curved. The markings on its surface radiate from the articular end. 



The preopercular {p-op) has the usual relations to the suspensorium, and there is 

 nothing peculiar about its form. The sculpturings on its surface radiate from a point 

 near its middle. 



The suhopercular (s.op) is a small bone, also very thin and papery, and is marked 

 with ridges which radiate from its lower and anterior corner. 



The interopercuJar {i-op) is a greatly elongated bone, truncated at its posterior, 

 pointed at its anterior end, and marked with ridges which radiate from a point near 

 the junction of its anterior and middle thirds. 



4. The Hyoidean Apparatus. (Plate IV. figs. 14-16.) 



This is of rather unusually small size as compared either with the suspensorium or 

 with the branchial arches ; the two cornua of which it consists are short and wide, and 

 contain the normal number of ossifications. 



The interhyal [i.hy) is a small rod-like bone, tipped with cartilage, which joins each 

 hyoidean cornu to the synchondrosis between the hyomandibular and symplectic. 



The epihyal {ep.hy), or dorsalmost ossification of the cornu proper, is of somewhat 

 triangular form. 



The ceratohyal (c.hy) is a very irregular bone, forming the main part of the cornu, 

 and separated by a cartilaginous interval from the epihyal. 



The hypohyals (h.hy) are two short nodular bones, attached to the inner face of the 

 distal or lower end of the ceratohyal, and separated from one another by cartilage. 

 The hypohyals of opposite sides are separated from one another by the glossohyal, a 

 median ventral element of the hyoid arch (figs. 6 and 17, c/j'): this will, however, be 

 more conveniently considered along with the branchial arches. 



The Iranchiostegal rays (br.r). — These are six sabre-shaped bones attached by 

 membrane to the outer face of each hyoidean cornu near its posterior border. The 

 first or dorsalmost of the series (br.r^) is connected with the epihyal, the other five 

 with the ceratohyal. They diminish progressively in length from above downwards, 

 the first being a little more than 5 inches long, while the lowest or distal ray (br.r ^) 

 is hardly more than 1^ inch. 



The urohyal or basi-branchiostegal (fig. 6, u.hy) is a flat unpaired bone nearly 4 inches 

 long, placed upright below the ventral ends of the hyoidean cornua. 



