66 MAMMALIA. 



It seems very probable that the teeth with enamel crowns, known 

 as Scaldicetus, will eventually prove to be the same as those called 

 Eucetus t the latter, it may be, having lost their crowns. 



Eucetus amblyodon is now recognised from the Nodule-bed of 

 the Red Crag of Suffolk and from the Antwerp Crag. 



Genus BALJENODON, Owen, 



BALJSNODON PHYSALOIDES, OWEN. 



PLATE VII., FIGS. 2. b, 3a, b. 



Sir R. Owen (Brit. Foss. Mamm. p. 536, 1846) described a 

 portion of a large Physeteroid tooth from the Red Crag of 

 Felixstow, which on account of the slender core of dentine and 

 thick cement, he regarded as distinct from the recent Cachalot, 

 and named Balcenodon physaloides. That the tooth thus named 

 is distinct from that of the Cachalot is not doubted ; but 

 Mr. Lydekker (Quart. Journ. Geol. Soc., Vol. XLIIL, p. 14, 

 1887) thinking that it was identical with Scaldicetus Carreti, 

 Dn Bus (Bull. Ac. Roy. Belg., Ser. 2, Vol. XXIV., p 568, 1867), 

 questioned the correctness of the original description. 



Prof. Lankester (Quart. Jourri. Geol. Soc., Vol. XXL, p. 231, 

 1865) noticed the Crag teeth which had been very generally 

 referred to Balcenodon physaloides, and called attention to the 

 probability of the larger forms being closely related to the teeth 

 found in the Antwerp Crag, which Prof. Van Beneden considered 

 to belong to ziphioid forms of Cetacea, and which have since 

 been named Eucetus amblyodon by Du Bus. 



The type specimen of Balcenodon physaloides is preserved in 

 the British Museum, and fresh microscopic sections having been 

 prepared, Mr. Lydekker and I have carefully examined them 

 and we are now able to confirm the description and figures given 

 by Sir R. Owen (loc. cit) The slender cylinder of dentine is 

 remarkable, leading one to think when first examining the tooth, 

 that the whole of the specimen was dentine, and Mr. Lydekker 

 has expressed this opinion (Quart. Journ. Geol. Soc., Vol. XLIIL, 

 p. 14, 1887) but an examination with a microscope shows that 

 the thick outer coating is cement, as stated by Sir R. Owen, and 

 resembles the cement of other Physeteroid teeth in having largely 

 developed *' Sharpey's Fibres " as well as closely set lacunae. 

 By the courtesy of M. Dupont of the Brussels Museum we have 

 been able to compare microscopic sections of the tooth of Scaldi- 

 cetus Carreti, and we are able to confirm Mr. Lydekker's statement 

 (loc. cit.)) that the dentine of this tooth is thick like that in 

 Eucetus, and, therefore, as we now find, unlike the slender form 

 which it has in Balcenodon physaloides, and Scaldicetus is regarded 

 as distinct from Balcenodon, whatever may be its relationship to 

 Eucetus. 



There are three teeth from the Red Crag of Suffolk in the 

 Museum of Practical Geology, which having been cut through 



