The details of structure vary greatly among the different species, for which reason almost every species has been properly made the type of a distinct genus. The two species found in Japan are _Ditrema temmincki_ and _Neoditrema ransonneti_. In the latter species the female is always toothless. Close to _Ditrema_ is the blue surf-fish of California, _Embiotoca jacksoni_, the first discovered and perhaps the commonest species. _Tæniotoca lateralis_ is remarkable for its bright coloration, greenish, with orange stripes. _Hypsurus caryi_, still brighter in color, orange, green and black, has the abdominal region very long. _Phanerodon furcatus_ and _P. atripes_ are dull silvery in color, as in _Damalichthys argyrosomus_, the white surf-fish, which ranges northward to Vancouver Island, and is remarkable for the extraordinary size of its lower pharyngeals. _Holconotus rhodoterus_ is a large, rosy species, and _Amphistichus argenteus_ a large species with dull yellowish cross-bands. _Rhachochilus toxotes_ is the largest species in the family and the one most valued as food. It is notable for its thick, drooping, ragged lips. _Hyperprosopon arcuatus_, the wall-eye surf-fish, is brilliantly silvery, with very large eyes. _H. agassizi_ closely resembles it, as does also the dwarf species, _Hypocritichthys analis_, to which the Japanese _Neoditrema ransonneti_ is very nearly related. The other species are all small. _Abeona minima_ and _A. aurora_ feed on seaweed. _Brachyistius frenatus_ is the smallest of all, orange-red in color, while its relative, _Zalembius rosaceus_, is handsomest of all, rose-red with a black lateral spot. _Cymatogaster aggregatus_, the surf-shiner, is a little fish, excessively common along the California coast, and from its abundance it has been selected by Dr. Eigenmann as the basis of his studies of these fishes. In this species the male shows golden and black markings, which are wanting in the silvery female, and the anterior rays of the anal are thickened or otherwise modified. No fossil embiotocoids are recorded. The viviparity of the Embiotocidæ was first made known by Dr. A. C. Jackson in 1863 in a letter to Professor Agassiz. From this letter we make the following extracts: