PISCES. 69 



More than half the known species of this genus are from the southern 

 hemisphere, principally round the southern coast of Africa. 



Add genera Pristiurus BONAP., Hemiscyllium MUELL. and HENLE, 

 Chiloscyllium MUELL. and HENLE, Crossorhinus MUELL. and HENLE, 

 (ringlymostoma MUELL. and HENLE (Nebrius RUEPPELL), Stegostoma 

 MUELL. and HENLE. 



ORDER IY. Eleutherobranchii s. Holocephali. 



Branchiaj not affixed by their outer margin, covered "by an oper- 

 culum, emitting the water by a single aperture on each side behind 

 the head. Dorsal cord persistent. 



Family VI. Chimceroidei. Cranium fibroso-cartilaginous, con- 

 tinuous, produced below on each side into an articular process for 

 the lower jaw. Operculum small, adhering to the hyoid arch, sus- 

 taining rays posteriorly. Rays of branchiostegous membrane flat, 

 concrete at the base, conjoined with the rays of operculum, and 

 contiguous to them. Four fissures between the branchiae on each 

 side. Temporal foramina none. 



These fishes approach the sharks very nearly, but are distinguished 

 by many aberrant characters from these and all other fishes. In the 

 rest of the fishes that have a lower jaw this is always connected 

 with the cranium by one or more separate bones (os quadratum or 

 suspens&rium) ; in Chimcera such a distinct bone is not present, but 

 is replaced by a process from the cranium. Also the bones of the 

 upper jaw and the palate are fused with the skull, without any 

 separation or traces of suture. The cJiorda dorsalis presents nume- 

 rous small cartilaginous rings in its sheath, and in this way offers 

 some resemblance to an aspera arteria; cartilaginous laminae (much 

 less numerous than these rings) form the arches of the vertebral 

 column (neurapophyses). The anterior part of the column, with 

 which the skull is connected by articulation, is flatter and formed 

 of a single piece ; above this is a perpendicular cartilaginous lamina 

 to which the large spine, situated in front of the first dorsal fin, is 

 affixed. 



See SCHULTZE in MECKEL'S Archiv fur die Physiol. rv. s. 348, Tab. rv. 

 fig. 3, and the figure of the skeleton of Chimcera monslrosa in ROSENTHAL 

 Ickthyot. Tafeln, xxvu. Compare with this especially J MUELLER in his 

 Vergl. Anatomic der Myxinoiden, i. 1835, s. 136 138, s. 153 159, Tab. 

 v. fig. i, 2 (two skulk of Calloi-Jiynchus). 



