GET ACE A. 67 



longitudinally show a slender core of dentine similar to that of 

 the type of Balcenodon physaloides. One of these agrees in form 

 also very closely with the type, and although about one third 

 smaller can only be referred to that species. 



The other two differ somewhat in shape, one being nearly 

 cylindrical, much curved, measuring 110 mm. in length and 

 19 or 20 mm. in width, tapering only slightly at each end ; while 

 the third example is nearly straight, spindle-shaped, due to the 

 great development of cement in the middle where the diameter 

 is 34 mm. the length being 120 mm. In both these teeth the 

 dentine is a little thicker at the upper part of the tooth than at 

 the base ; and in the smaller tooth, which has the thickest core of 

 dentine, the greatest diameter of the dentine is 8*5 mm. 



Bearing in mind the exteme variation in form among the teeth 

 of the recent Pliyseter macroccphalus it is thought best to refer 

 all three specimens to Balcenodon physaloidcs, which at present 

 is only known from the Nodule-bed of the Red Crag of Suffolk. 



Genus PHYSETERULA, V. Beneden. 

 PHYSETERULA DUBUSII ? v. BENEDEN. 



This genus and species was established by Prof. Van Beneden 

 (Bull. Ac. Eoy. Belg., Ser. 2, Vol. XLIV., p. 851, 1877) for a 

 lower jaw from the Antwerp Crag, about 45 inches long containing 

 numerous teeth, the largest of which were perhaps five inches in 

 length. Mr. Lydekker provisionally refers to this species a tooth 

 from the Red Crag (Nodule-bed) of Woodbridge, now in the 

 British Museum (No. 49,966, Cat. Foss. Mamm., Part v, p. 54, 

 1887) which he had previously referred to Homocetus Villersi 

 (Quart. Journ. Geol. Soc., Vol. XLIII. p. 14, 1887). 



The great variety of forms which occur among the teeth of the 

 recent Sperm Whales, and even among the teeth of one individual 

 makes it highly probable that the Crag teeth, in which the develop- 

 ment of cement was greater than in the living species, varied to 

 as great if not to a greater extent, and consequently it is highly 

 probable, as already suggested by Profs. Van Beneden and Gervais 

 (Osteogr. Cetaces, p. 345, 1880) that many of the forms from the 

 Antwerp Crag, which have been named as several distinct genera 

 and species will eventually prove to belong to only a few species. 

 Under these circumstances 1 should have hesitated before intro- 

 ducing some of these n a mes into English literature ; but as Mr. 

 Lydekker has already done so, the present and five following 

 species are provisionally and doubtfully accepted on his authority. 



E 2 



