1. CHOIUSOCIIISMUS. 493 



culum is the largest piece of the opercular apparatus ; its anterior 

 limb is entirely covered by the tjTnpanic, and its angular portion is 

 much produced backwards and pro\-ided with a strong ridge ; inter- 

 operculum feeble, situated at the inner side of the proeoperculum ; 

 suboperculum composed of thi-ee processes, the posterior of which 

 terminates in a hook-like spine. The basal portion of the operculum is 

 solid ; the margin thin, cartilaginous. Glossohyal rudimentarj' ; bones 

 of the branchial arches thin and rather feeble ; basibranchials absent ; 

 pharyngeals separated, and armed with coarse cardiform teeth. 



The suprascapula and the scapula are simple styliform bones ; the 

 vertical portion of the humerus is as long as the horizontal ; the ulna 

 and radius are shorter than, and very similar to, the carpal bones. 

 The coracoid is well developed, and, as usual, composed of two pieces, 

 the upper of wliich is not suspended from the humenis, but fixed 

 by a ligament to the hinder margin of the carpal bones ; it is a 

 broad lamella dilated posteriorly into the cartilage, which is externally 

 visible ; the lower piece is narrower, and fixed to the extremity of the 

 pubic bone of its side. The pubic bones are imited by sutui'e, and 

 form together a heart-shaped disk, the point of which is produced 

 backwards. The anterior portion of the disk is concave, with a bony 

 longitudinal bridge and a feeble transverse ridge. The disk is fixed 

 to the humeral bones by the convex portions of its anterior margin, 

 whilst the convex portions of the lateral margins serve as base for 

 the ventral fins*. The latter are composed of one spiuc, which is 

 transformed to a broad thin and curved plate hidden below the skin, 

 and apparently of four rays ; but on closer examination we find that 

 the hidden ray has a longitudinal groove anteriorly, in which another 

 thinner ray lies concealed ; this ray is quite free, and not joined to 

 the pubic bone. We are not aware of another example of a similar 

 structui-e in fishes. 



The vertebral column is composed of fourteen abdominal and seven- 

 teen caudal vertebrae, the abdominal portion being rather longer than 

 the caudal. The first vertebra is thrice as broad as long, with its 

 three conical depressions very distinct and situated in the same hori- 

 zontal line ; the other vertebra) become more and more compressed 

 posteriorly. The neural and haemal spines are of moderate length 

 and strength, slightly inclining backwards. The zygapophyses of the 

 abdominal vertebrae are more developed than is usual in this Order, 

 whilst the parapophyses are entirely absentt. The ribs, which are 

 rather broad and horizontally du-ected outwards, are joined into tlie 

 lateral concavity of the vertebrae, immediately below the zygapo- 

 physes. The epipleurals are not much less developed than the ril s 

 from the extremities of which they are suspended and directed back- 

 wards. We might also consider the ribs as long and detached par- 

 apophyses, and the epipleuraLs as the ribs proper. The intcrneurals 

 and interha3mals are very feeble. 



* The structure of the ventral disk has not yet been correctly described. 

 Stannius, for instance (p. 91), denies the presence of the coracoid. Tlie ventral 

 fins have been taken for a detached portion of the pectorals, &c. 



t Stannius, I.e. p. 34 {Cott/lis). 



