26 PROCEEDINGS OF THE NATIONAL MUSEUM. voi.. 03. 



Icoth on the left side possesses the longest enamel crown (10 mm.), 

 while the first tooth on the right side has the broadest crown (5 mm.). 

 The smallest tooth has an enamel crown 7 mm. long and a maxi- 

 mum diameter of 3 mm. 



Skulls of Lifotes and Inia possess teeth whose enamel crowns are 

 strongly rugose. The surfaces of the enamel crowns of these fossil 

 teeth are ornamented with fine longitudinal striae ; those of a young 

 Platanista skull are smooth. In case of old individuals of Platanista 

 the enamel crowns of the teeth almost always show the effects of wear 

 and on many of the teeth the enamel is entirely missing. The crowns 

 cf the teeth of this fossil porpoise and those of Platanista are com- 

 pressed antero-posteriorly. There is no well defined neck between the 

 expanded portion of the root and the enamel crown. The swollen 

 part of the root of many of the teeth has a greater diameter than 

 that of the crown. There is no indication of a cingulum. The distal 

 extremities of the roots are slender, elongated, and curved backward. 

 The mandibular teeth are similar to the maxillary teeth in form, but 

 the crowns of the posterior teeth are relatively smaller. « 



HYOID BONES. 



The hyoid bones bear some resemblance to those of the Delphinidae, 

 especially Phoeaena. Although the basihyal and the two thyrohyals 

 are ankylosed (pi. 9, fig. 1), the sutures between the component parts 

 are apparent. The central portion (basihyal) is strongly compressed 

 dorso-ventrally and possesses two short, anterior, conical projections 

 (ceratohyals) which were joined in front by cartilage with the elon- 

 gate stylohyals. The expanded lateral wings (thyrohyals) of the 

 hyoid bone curve backward and upward, but their distal ends are 

 bent downward. These thyrohyals are subcrescentic in outline, rela- 

 • ively thin, concave superiorly, and convex inferiorly. Internally 

 there is a slight elevation or ridge which marks the line of fusion of 

 thyrohyal with the basihyal. The antero-external margin of either 

 thyrohyal is recurved and to it were attached the stylohyoid liga- 

 ments. 



The ankylosed basihyal and the two thyrohyals of this fossil por- 

 poise are similar in some respects to those of Inia geojfrensis. They 

 differ widely from the figure given by Anderson^ for those of Plata- 

 nista^ which shows the thyrohyals dilated at their basihyal ends 

 instead of mesially, the presence of free elongate rodlike ceratohyals, 

 and the absence of posterior projections on the basihyal. Small pos- 

 terior projections are present on the basihyal of this fossil hyoid. 



s Andeison, J., Anatomical and Zoological Researches: Comprising an account of the 

 Zoological Results of the Two Expeditions to Western Yunnan in 186S and 1875. Lon- 

 don (1878), p. 528 pi. 40, fig. 20. 1879. 



