12 ME. E. LYDEKKEE ON THE CETACEA OF THE SUFFOLK CEAG. 



greater inflection, greater height of the inner wall, smaller depth of 

 the Eustachian notch, sharper posterior angle, and more gibbous m- 

 volucrum, there is little doubt of its specific distinctness, and every 

 probability of its being identical with the so-called B. Sibbaldina,Y&Ti 

 Eeneden, of which the tympanic has been hitherto unknown. This 

 is confirmed by a very fine late cervical vertebra from the Red Crag 

 in the Ipswich Museum, which corresponds exactly with the type 

 specimens of the latter form in the Brussels Museum. The rather 

 smaller B. Goropi, Yan Beneden *, is represented by an imperfect 

 tympanic from the Red Crag, in the British Museum (No. 39016), 

 and probably by some vertebrae in the same collection. Of the still 

 smaller B. borealina, Yan Beneden, there is an imperfect tympanic 

 (of which the British Museum has a cast) in the Ipswich Museum, 

 from the Red Crag, as well as two similar specimens in the British 

 Museum (Nos. 3907-8). The next form is that named by Owen 

 Balcena emarginata (with which B. gibbosa, Owen, appears to be 

 identical f), which is represented by several tympanies in the Museum 

 of the College of Surgeons %, and by one in the British Museum 

 (No. 39016 a) ; these specimens are absolutely undistinguishable 

 from the tympanies found in the Antwerp Crag, which Yan Beneden 

 has named Balcenoptera rostratella, a name which must give place 

 to the earlier one applied by Owen, so that the species must be 

 known as Balcenoptera emarginata. With regard to the genus 

 Plesiocetus of Yan Beneden, I think it advisable to adopt Brandt's 

 view of including it in his genus Cetotlierium, with which Hetero- 

 cetus §, Yan Beneden, may also apparently be grouped. The 

 tympanic is readily distinguished from that of Balcenoptera by its 

 anteriorly pointed form, the triangular shape of the roughened 

 inferior surface, and the less flattened involucrum. To C. Brialmonti 

 (Yan Beneden) I refer an imperfect axis-vertebra from the Red 

 Crag, in the British Museum (No. 46734) ; while the smaller C. 

 clubium (Yan Beneden) is represented by two imperfect tympanies in 

 the Museum of the College of Surgeons (Nos. 2852, A and B)|j, and 

 probably by some periotics in the British Museum (e. g. No. 30261). 

 Some vertebrae in the latter collection probably belong either to this 

 species or to C. Burtini (Yan Beneden) ; while others which belong 

 either to the latter or to C. Hupselii (Yan Beneden) I have 

 provisionally referred to the last-named species. The still smaller 

 C. brevifrons (Yan Beneden %) is represented by an axis-vertebra 

 in the British, and another in the Ipswich Museum, while it is not 



* Syn. B. musculoides, Yan Beneden ; the reasons for adopting the former 

 name will be given in the Cat. Foss. Mamm. Brit. Mus. pt. v. 



t The form of the involucrum on which Owen distinguished this second 

 species alters with age. 



J Nos. 2822-2825. Some of the other specimens included under the same 

 head are distinct. 



§ This is really not more than a MS. name. 



| These numbers do not appear in the published ' Catalogue,' but have been 

 entered in MS. by Dr. Garson in the Museum copy. 



Syn. Heterocetus brevifrons. The type specimens are not figured, and I 

 have identified the English examples by comparison with those in the Brussels 

 Museum. 



