80 



Recherches sur les Poissons Fossiles. 



of the vertebral column at the base of the caudal fin, in the 

 fishes of the present day. 



Tetragonolepis dorsalis, Ag., and Tetragonolepis ovalis, 

 id. PI. IV. The genus to which these species belong, differs 

 only from Dapedius (of which we have already given an 

 example) in the form of the teeth, these being in Dapedius 

 somewhat grooved and blunt, and in the present genus, 

 pointed. The osteology does not appear to M. Agassiz to be 

 essentially different in the two genera ; the head in particu- 

 lar presents the closest analogy, the bones having the same 

 connection, the jaws the same form, only that the teeth 

 are pointed in the present genus, instead of being grooved as 

 in Dapedius. Tetragonolepis comprises numerous species ; 

 above seventeen are already figured and described by M. 

 Agassiz. They nearly all belong to the lias formation, there 

 being but a single species found in the inferior oolite resting 

 on the lias. Many of the specimens examined were from 

 Lyme Regis in England, but some were also from various 

 parts of Europe. 



Tetragonolepis ovalis, one of the examples, Plate IV, is from the 

 lias formation of the vicinity of Boll in Switzerland, where it 

 was examined by M. Agassiz, in the Museum of Dr. Hartmann of 

 Goeppingen, by whom it was discovered. The peculiarities which 

 distinguish it from other species, are rather differences of general form, 

 than of particular details. It is more elongated than any other 

 species of the genus known to M. Agassiz ; it is oval anteriorly, 

 more elongated, and straitened towards the tail. The head is propor- 

 tionally smaller, and considerably more elongated than any of its 

 congeners. Its mouth is also a little more cleft, and its teeth are 

 also more elongated than in other species, and have all their points 

 uniform „ The bones of the head in the example Uthographed, are 

 only visible on the inner part of the face at the left side. At the 

 inferior margin of the inter- opercule and sub-opercule, we see seven 

 large flat branchial rays. What is most curious in this example 

 is, that portion of the branchial arches and the combs of the branchies * 



