]68 LEPIDOSIREN. 



dental plate, but is narrower in the upper one. The figures 1, 2 

 and 3, PI. 59, which give respectively a side view, front view and 

 the working surfaces of the teeth of the Lepidosiren, will convey a truer 

 idea than can be given by words, of the form of the maxillary dental 

 plates. The two anterior lobes or divisions of both upper and lower 

 dental plates are the most produced in the vertical direction, and their 

 anterior angle is pointed and adapted for piercing. The posterior 

 divisions are most extended in breadth and least in height, and 

 terminate in a sharp trenchant edge ; the middle lobes present an 

 intermediate structure. 



These teeth, in their paucity, large relative size, and mode of 

 adaptation to the jaws, resemble the dental plates of the Chimseroid 

 and some of the extinct Hybodont cartilaginous fishes, as Cochliodus 

 and Ceratodus Ag. ; but they are unlike these in microscopic structure; 

 approaching in this respect, as will be presently shown, nearer to 

 the teeth of many osseous fishes. The maxillary armour of the Lepi- 

 dosiren surpasses any known dental apparatus in the class of fishes in 

 the modification of the working surface, by which a single tooth is 

 at once adapted for piercing, cutting and crushing the alimentary 

 substances. The strength of the jaws of the Lepidosiren and 

 the bulk of the muscles which work them are proportionate to 

 the size and nature of the maxillary dental plates. 



In PI. 59, fig. 4, is given a reduced representation of a magnified 

 view of a vertical section of a lobe of the lower dental plate of the Lepi- 

 dosiren. It consists, as in the cod and sphyrsena, of a central mass of 

 coarse osseous substance, traversed by large and nearly parallel 

 medullary canals, and an external sheath of very hard enamel-like 

 dentine. The medullary canals are continued from a coarse reticula- 

 tion of similar, but wider canals, in the substance of the supporting 

 bone, and advance forwards, nearly parallel with each other, and 

 with the plane of the upper surface of the tooth ; they anastomose 

 together by short, curved, transverse canals, which intercept spaces 

 increasing in length as the canals recede from the osseous basis. 

 The canals themselves diminish in size in the same ratio, and when 

 they have arrived near the dense outer layer, their divisions and 

 inosculations become again more frequent, the peripheral loops form- 



