Isospondyli 53 



figured. Numerous herring, referred to Clupea, but belonging 

 rather to Pomolobus, or other non-Arctic genera, have been 

 described from, the Eocene and later rocks. 



Several American fossil herring-like fishes, of the genus 

 Leptosomus, as Leptosomus percrassus, are found in the Cretaceous 

 of South Dakota 



Fossil species doubtfully referred to Dorosoma, but perhaps 

 allied rather to the thread-herring (Opisthonema), being herrings 

 with a prolonged dorsal ray, are recorded from the early Ter- 

 tiary of Europe. Among these is Opisthonema doljeanum from 

 Austria. 



The Dorosomatidae. The gizzard-shad, Dorosomatida, are 

 closely related to the Clupeida, differing in the small contracted 

 toothless mouth and reduced maxillary. The species are deep- 

 bodied, shad-like fishes of the rivers and estuaries of eastern 

 America and eastern Asia. They feed on mud, and the stomach 

 is thickened and muscular like that of a fowl. As the stomach 

 has the size and form of a hickory-nut, the common American 



FIG. 42. Hickory-shad, Dorosoma cepedianum (Le Sueur). Potomac River. 



species is often called hickory-shad. The gizzard-shad are all 

 very poor food-fish, bony and little valued, the flesh full of 

 small bones. The belly is always serrated. In three of the 

 four genera of Dorosomatidce the last dorsal ray is much produced 

 and whip-like. The long and slender gill-rakers serve as strainers 

 for the mud in which these fishes find their vegetable and ani- 

 mal food. Dorosoma cepedianum, the common hickory-shad or 



