MESOPLODON. 89 



6. Tympano-periotic bones, right, from the Shetland skull, 

 June 1885, No. 2. Length If inch, breadth 1 inch, 

 height 1 inch. Stapes not ankylosed. The Tympanic 

 has the outer surface moderately convex, marked by 

 a vertical groove into a large anterior and smaller 

 posterior divisions, the anterior being 1^ inch in 

 length. Lip-like process extending down outer 

 surface. Inner surface, f inch deep, is faintly 

 striated and not sharply divided into an anterior and 

 a posterior part, but gradually diminishes in thick- 

 ness from behind forwards. The inferior aspect is 

 bilobed at posterior end, the outer being larger than 

 the distinct inner lobe; the groove of separation 

 expands anteriorly into a shallow roughened fossa; 

 from its breadth this aspect forms an inferior surface ; 

 the cavity opens close to the anterior end of this 

 surface. See figure of inferior surface. The Periotic 

 is 1| inch long and | inch broad. See Turner, Journ. 

 Anat. and Fhys., vol. xx., 1886. 



7. Tympano - periotic bones, right, detached from the 



Morrison's Haven skull, No. 5. The stapes is not 

 ankylosed to the periotic bone. 



8. Periotic bone, left, from No. 4. Stapes in situ but not 



ankylosed. 

 Shetland, 1881. 

 1). Tympano-periotic bones, left, from No. 3. Stapes not 



ankylosed to periotic. 

 Firth of Forth, Dalgety Bay. 



10. Tooth extracted from mandible and vertically cut to 



obtain slices for microscopic examination. Described 

 and figured by Turner in the Challenger Reports, 

 vol. i., 1880. Challenger Collection. 



11. Teeth, casts of two mandibular, of Sowerby's Whale, 



probably adult. 



