Recherches sur les Poissons Fossiles. 343 



the 3rd genus also consists of but one known species, the 

 remains of which are found in the lias of Boll in Switzerland. 



The 4th genus, Sauropsis, comprises but two establish- 

 ed species : one from the Zechstein of Sohlenhosen, the other 

 from the lias of Wirtemberg and Baden. The 5th genus, 

 Pachycormus, Agassiz, afTords three species, one from Soh- 

 lenhosen, and two from the lias of Beaune in Bourgoyne 

 and Wirtemberg. The 6th genus, Thrissops, Agassiz, two 

 from Sohlenhosen, and one of a Jurasic structure, but lo- 

 cality unknown. The 7th genus, Urceus, Agassiz ; con- 

 sists of five species, all from the Zechstein of Sohlenhosen ; 

 the 8th genus Leptolepis, Agassiz, consists of seven species, 

 of which four are from the lias of various parts of Europe, and 

 two from Sohlenhosen. The 9th genus, Megalurus, Agas- 

 siz, is founded on a single species found at Sohlenhosen. 

 The 10th genus, Saurostomus, is founded also on a single 

 species from the lias; and of the 11th genus, Aspidor- 

 hynchus, Agassiz, one is from the lias, and two species from 

 Zechstein of Sohlenhosen. 



The 3rd family, or Pycnodonts, like the two preceding 

 families, has no one representative in the present creation. 

 Those genera in which the superior spines of the caudal 

 vertebrae are elongated, causing a corresponding elongation 

 in the upper lobe of the caudal extremity, are anterior to the 

 Jura deposits. The first genus of this family, Placodus, 

 Agassiz, embraces two species, one from the Muschelkalk 

 at Bayreuth, and one from the Gres Bigarre at Deux Points. 



Of the 2nd genus, Sphoerodus, Agassiz, one is found in 

 Zechstein at Sohlenhosen ; one above the Jura formation ; 

 two in the chalk formation ; and two in the tertiary beds 

 at Aix and Lonjameau respectively. The third genus 

 Gyrodus, Agassiz, comprises five species ; two of which are 

 found in the upper Jura rocks ; one in the chalk of Caen and 

 at Baden, and one in the Speeton clay, Yorkshire ; and one 

 locality unknown. The fourth genus, Microdon, Agassiz, 



