Mr. Owen on the Zeuglodon Cetoides. 75 



radiating in the section examined from two centres, one in each lobe, without 

 any intermixture of coarser medullary tubes, such as characterize the teeth of the 

 Iguanodon, and without the slightest trace of the reticulate canals which distin- 

 guish the texture of the teeth of the Shark, the Sphyrcsna and its congeners. 



The breadth of the calcigerous tubes in the Zeuglodon is equal to one-eighth of 

 the diameter of an ordinary human blood-disk or globule ; they present a regular 

 undulating course, and, like the calcigerous tubes of the Dugong, exhibit more 

 plainly the primary dichotomous bifurcations, and the subordinate lateral branches, 

 which are given off at acute angles. 



Upon the whole, the microscopic characters of the texture of the teeth of the 

 Zeuglodon are strictly of a mammiferous character, and the nature of their investing 

 substance limits the comparison of these teeth with those of the few Mammalia 

 in which the teeth are devoid of enamel. Among these are the Edentata, inclu- 

 ding the Megatherium and its congeners, the Morse, the Dugong and the Cachalot. 

 The tooth of the Megatherium contains two kinds of dentine ; the first is a coarse 

 central portion with large medullary canals, giving off the short calcigerous tubes 

 which occupy the interspaces of the canals, similar to the substance which composes 

 the entire tooth of the Orycteropus ; and the second is a fine and dense dentine, com- 

 posed of minute parallel calcigerous tubes. The ceementum of the Megatherium 

 is also distinguishable by the large medullary canals which traverse it, and which 

 anastomose by loops close to the true or dense ivory. We have therefore suffi- 

 cient evidence that the Zeuglodon is not a gigantic edentate Mammal. 



From the Toxodon it differs in the fangs of its teeth, and also in the fact that 

 the teeth of the Toxodon are partially covered with true enamel. 



It is to the teeth of the Cachalot and Dugong that those of the Basilosaur offer 

 the nearest resemblance in the particulars already cited, and I conceive its position 

 in the natural system to have been in the cetaceous order, intermediate between 

 the Cachalot and the herbivorous species. 



Dr. Harlan, who has examined with me the sections of the various teeth above 

 alluded to, and who is willing to admit the arguments deducible from them in 

 favour of the mammiferous nature of the Basilosaur, has himself suggested the 

 propriety of substituting another generic name more in accordance with the true 

 affinities of the animal, and has consented that the gigantic monarch, as it was 

 deemed, of the saurian race, should be deposed*. 



* 'J'he fragments of jaw and teeth, humerus, and fragments of rib, were discovered in a limestone rock, 

 supposed to belong to a formation more recent than the Maestricht beds, in the Alabama territory. The 

 vertebrae of the Zeuglodon were discovered by Judge Bree in a tertiary stratum, associated with con- 

 glomerate masses of small marine shells, principally belonging to an extinct species of Corhula ; they were 

 imbedded in a hill about two hundred yards from the Owachita or Washita river, Arkansas territory, in 

 the state of Louisiana. The circumstances which led to their discovery are thus described : — 



l2 



