142 GOBIID^. 



K. Adult male : skeleton : not good state. Purchased. 



X. Adult male : skeleton. Polperro. Presented by J. Couch, Esq. 



Skeleton. — The skeleton of CaUiomjmus resembles that of the 

 typical Gohiina with regard to the form of the cranium and the 

 thin osseous layers of the single bones, but shows several very re- 

 markable peculiarities : — 



1, in the structure of the facial bones ; 



2, in the arrangement of the opercular bones ; 

 3; in the structure of the humeral arch ; 



4, in the three joints between occipital and first vertebra, situated 

 on the same horizontal line ; 



5, in the small number of vertebrae. 



The great protractility of the jaws is effected by the extreme pro- 

 longation of the processes of the intermaxillary bones ; they are 

 much longer than the body of the bones, moving in a broad shallow 

 gro(\ve formed by the ethmoid, nasal and prsefrontal bones, and ex- 

 tending backwards in a cavity of the interorbital space. They are 

 slightly curved, so that when the upper jaw is protracted, it assumes 

 a downward direction. The maxillary is shorter than the inter- 

 maxillary and scarcely dilated ; its extremity is received in a shallow 

 groove formed by a vertical ridge of the posterior portion of the 

 mandibula. The mandibles are long, slender, the symphysial angle 

 being rather acute. The praeorbital is thin, very long, extending 

 nearly to the end of the snout ; infraorbital bones none. The an- 

 terior part of the vomer projects into the mouth, and its body is 

 rather broad and flat, tapering posteriorly. The pterygoid bones are 

 very narrow, the pretympanic and mesotympanic very small, leaving 

 a very wide and free space below the large orbit. The hypotym- 

 panic is elongate, and has a very strong longitudinal crest ; it is as 

 long as the praeoperculum ; the latter has no ascending, only a hori- 

 zontal, limb, the former part being entirely replaced by the epitym- 

 panic ; immediately behind the epitympanic there is the narrow 

 operculum, which is much smaller than the suboperculum. The sub- 

 operculum is similar in form to an operculum, and occupies the space 

 in which, in other fishes, the latter bone is usually found ; it is very 

 thin, striated, and has the margin fringed. The interoperculum is 

 continuous with the suboperculum, forming a narrow, thin, elongate 

 lamella. 



The hypotympanic and the praeoperculum are provided with a 

 bony keel or crest, which extends from the joint of the mandible to 

 the base of the praeopercular spine ; another bony keel runs down- 

 wards from the joint of the epitympanic to the same spot, meeting 

 the first keel at an acute angle. It is evident that these two keels 

 serve to support the praeopercular spine : this would have been far 

 less the case if they had met at a right angle ; but in the direction 

 in which they are placed, they answer fully the same purpose as 

 that peculiar process which is found on the cheek of the true Cottoids. 

 Branchiostegals filiform. 



The crown of llie head is rather flat, about twice as broad as long. 



