_Syngnathus_ (M.), _Hippocampus_ (M.), _Solenognathus_. _Triacanthus_, _Monacanthus_, _Ostracion_. 3. The _Californian_ district includes a marked northern element, the principal constituents of which are identical with types occurring in the corresponding district of the Atlantic, viz. the North American, as exemplified by _Discoboli_, _Anarrhichas_, _Centronotus_, _Cottus_, _Hippoglossus_, _Clupea_ (_harengus_), etc. But it possesses also, in the greatest degree of development, some types almost peculiar to itself, as the _Heterolepidina_, some remarkable Cottoid and Blennioid genera, and more especially the Embiotocoids--viviparous Pharyngognaths--which replace the Labroids of the other hemisphere. Gadoids are much less numerous than in the North American district. The southern forms are but little known, but it may be anticipated that, owing to the partial identity of the Faunæ of the two coasts of the Isthmus of Panama, a fair proportion of West Indian forms will be found to have entered this district from the south. The following are the principal genera:-- _Chimœra_, _Galeus_, _Mustelus_, _Triacis_, _Cestracion_, _Rhina_, _Raja_. _Serranus_; _Chirus_, _Ophiodon_, _Zaniolepis_; _Sebastes_; _Nautichthys_, _Scorpœnichthys_, _Cottus_, _Centridermichthys_, _Hemilepidotus_, _Artedius_, _Prionotus_, _Agonus_; _Cyclopterus_, _Liparis_; _Anarrhichas_, _Neoclinus_, _Cebidichthys_, _Stichœus_, _Centronotus_, _Apodichthys_; _Psychrolutes_; _Auliscops_. _Embiotocidœ_. _Gadus_. _Hippoglossus_, _Psettichthys_, _Citharichthys_, _Paralichthys_, _Pleuronectes_, _Parophrys_. _Osmerus_, _Thaleichthys_, _Hypomesus_; _Engraulis_, _Clupea_. _Syngnathus_. III.--THE EQUATORIAL ZONE. As we approach the Tropic from the north, the tribes characteristic of the Arctic and Temperate zones become scarcer, and disappear altogether: to be replaced by the greater variety of Tropical types. Of Chondropterygians, the _Chimœridœ_, _Spinacidœ_, _Mustelus_, and _Raja_, do not pass the Tropic, or appear in single species only; and of Teleosteans, the _Berycidæ_, _Pagrus_, the _Heterolepidina_, _Cottus_ and allied genera, _Lophius_, _Anarrhichas_, _Stichæus_, _Lepadogaster_, _Psychrolutes_, _Centriscus_, _Notacanthus_, the _Labridæ_ and _Embiotocidæ_, the _Lycodidæ_, _Gadidæ_, and marine _Salmonidæ_ disappear either entirely, or retire from the shores and surface into the depths of the ocean.