CLUPEOIDS. 137 



In the genus Osteoglossum, the dental system of which is shown 

 in the large middle figure of Plate 48, the intermaxillary bones (a) 

 form only a small portion of the median and superior margin of the 

 mouth; the remainder is completed by the superior maxillaries (b b), 

 which, with the premandibular bones in the lower jaw, are armed 

 with a single series of equal, small, conical and sharp-pointed teeth : 

 near the lax symphysis of the lower jaw, there is a second series of 

 similarly shaped retroverted teeth. The vomer and anterior part of the 

 palatine bones are beset with small acute teeth ; the posterior part 

 of the palatines and the entire lower surface of the pterygoids are 

 covered with villiform denticles, but there is a row of longer sharp- 

 pointed teeth at the inner border of each pterygoid bone. The broad, 

 long, and flat lingual bone, (e) , is covered with minute close-set pointed 

 teeth, converting the upper surface of the tongue, into a hard boney 

 rasp, whence the name of the genus. The branchial arches and the 

 inferior pharyngeals support villiform teeth. 



The genus Glossodus affords additional examples of those fishes 

 in which the body of the os hyoides is provided with tubercular 

 teeth which are opposed to similar instruments for crushing the 

 alimentary substances, attached to the body of the sphenoid and 

 to the pterygoid bones. The maxillary, vomerine, palatine, branchial 

 and pharyngeal bones, both superior and inferior, are beset with 

 minute villiform teeth. 



In the three preceding genera of South American tropical fresh-water 

 fishes the broad, long and flat dentigerous plate, into which one of the 

 median hyoid ossicles is developed, forms a striking characteristic of 

 their dental system, and I shall here describe similar dentigerous 

 plates, found fossil, in the eocene formation, called the ' London Clay,' 

 at the Isle of Sheppey.(l) 



As these remains have hitherto been met with detached and un- 

 connected with the other bones of the skull, and exhibit little more 

 than the dentigerous covering, it cannot be unequivocally determined 

 whether they are the dentigerous armature of a broad lower pharyn- 



(1) Specimens of these are preserved in the well known collection of Sheppey. Fossils of 

 J. S. Bowerbank, Esq., F.G.S., whose liberality in permitting their description on this, as on 

 many other occasions, I have gratefully to acknowledge. 



