476 DR. W. G. RIDEWOOD ON THE CRANIAL [DeC. 15, 



and a row of similar teeth occurs on the middle of the palatal 

 surface of the entopterygoid. 



Ojjercular Series (text-figs. 134 and 135 C, pp. 474, 475). — The 

 opercular bone is remarkably large ; the subopercular is compa- 

 ratively small, and extends foi'ward beneath the intei'opercular, 

 and is bound to the posterior part of the outer face of the epihyal 

 in such a way that it has a tendency, dui'ing the process of dis- 

 articulation of the skull prior to the maceration of the paiis, to 

 leave the opercular bone and to come away with the hyobranchial 

 skeleton. In such cases it is liable to be mistaken for the hinder- 

 most of the branchiostegal rays (text-fig. 135 0, p. 475), a fact 

 long ago noted by Valenciennes, who wrote (Hist. Nat. Poiss. xxi. 

 1848, p. 11) concerning the subopercular, " il faut faire attention 

 de ne pas le confondi-e avec un rayon de la membrane branchio- 

 stege." This is an argument in favour of regarding the opercular, 

 subopercular, and branchiostegal bones as components of one and 

 the same series, to which series the preopercular and interoper- 

 cular do not belong. 



The branchiostegal rays are usually ten in number on each 

 side, sometimes nine or eleven ; I have not seen as many as 

 thirteen, the number given by Valenciennes {I. c. p. 11) and 

 Gunther (Brit. Mus. Oat. Fishes, vii. p. 386). The first nine are 

 situated on the outer face of the whole length of the ceratohyal, 

 the last on the epihyal. They form a well-graduated series, and 

 are flat, not rod-like. When, as above mentioned, the sub- 

 opercular is left attached to the epihyal, it is seen that the 

 subopei'cular and the last branchiostegal i-ay resemble one another 

 closely in shape and size, but that there is some discontinuity in 

 the series owing to the interval between the subopei'cular and the 

 last branchiostegal ray being greater than that between the last 

 two branchiostegal rays (text-fig. 135 0, p. 475). 



Hyobranchial Series. — The intei'hyal is a long and rod -like bone 

 (text-fig. 135 A, p. 475). The hyoid is long, the posterior end of the 

 epihyal being close to the postei'ior end of the first cerato branchial. 

 The lower hypohyal is much larger than the upper, and excludes 

 the lattei- from union with the ceratohyal (text-fig. 135 0, p. 475). 

 The glossohyal is extremely reduced, and consists of a small cone 

 of cartilage, with a small cap of edentulous membrane-bone on its 

 upper surface. The urohynl is long and slender. 



A narrow membrane- bone, with crowded small teeth, extends 

 over the whole length of the second basibranchial, and pi-ojects 

 forwards over the postei'ior half or moi'e of the first basibi'anchial 

 and backwards over the anterior sixth of the third basibranchial. 

 The second basibranchial is remarkably long, a fact which disturbs 

 the parallelism of the first and second ceratobranchials. The 

 first hypobranchials ai'e long, almost as long as the first cerato- 

 branchials ; the second, however, are small and triangular, and 

 are fused with the sides of the posterioi- end of the second basi- 

 branchial. The third hypobranchials a,re normal, and slope 

 obliquely down the sides of the third basibranchial. 



