222 PLAXANISTID^. 



maxillary crests it resembles the Hyperoodon ; in the expanse of the 

 temporal fossaj, the strength of the zygomatic arches, the shortness 

 of the malars, and the smallness of the orbits, it is peculiar among 

 the true Cetacea. Contrary to the rule in the Deljihinklfp, the 

 anterior teeth retain their prehensile structure, while the posterior 

 ones soon have their summits worn down to their broad bases. The 

 implanted base of the tooth is remarkably expanded in the antero- 

 posterior direction, and its outer surface is augmented by longitu- 

 dinal folds like those of the teeth of Sauroid fishes, but weaker than 

 in them. Sometimes the posterior teeth are implanted by two short 

 fangs, which is a still more exceptional character in the existing 

 carnivorous Cetacea" (p. 449). 



The form of the crest of the skull is modified according to the age. 

 In the head of a young specimen in the Anat. Mus. Univ. Edin., 

 Knox Cat. n. 105, the reflexed portion of the maxillary bones is only 

 partially developed ; their inner sides are cellular, and radiately 

 ridged with a ragged edge. 



In the skull of a half-grown specimen in the Royal College of 

 Surgeons the crest is rather produced in front ; the upper part of 

 the front edge is suddenly raised behind, compressed, and foi-ms a 

 sort of ovate crest. 



In the skull of an adult the crest is regularly arched, and the 

 upper part of the front edge is obliquely truncated, as represented in 

 Cuvier, tom. cit. xxii, f. 8, and in Ann. & Mag. N. H. 1852, t. 5 & 6. 



"From the minuteness of its eyes, the Susu is obviously adapted 

 for turbid rather than clear water, and it has never been observed 

 out to sea." — Blyih. 



Mr. Blyth observes, " I have heretofore been under the impression 

 that the specimen presented [to the Museum of the Asiatic Society] 

 by M. Duvaucel was of the male sex, but I find it otherwise, and 

 certain discrepancies of proportion which I had suspected to indicate 

 sexual diversity may yet prove to be of specific importance. I 

 have never obtained a male of this animal. So far as can be judged 

 from apparently well-stufFed specimens, that of M. Duvaucel is of 

 a more slender form, with a longer rostrum, unUke any that I have 

 seen from the river Hougly. Entire length 6 feet to point of tail- 

 flukes, and 1 foot 5| inches from gape to tip of rostrum. Length of 

 Calcutta female 7 feet, with rostrum 13| inches from gape. The 

 two skulls presented by Dr. Wallich show a similar disparity." — Cat. 

 Mus. Asiat. Soc. 92. 



In the young specimens the ja^vs are rather swollen, and oblong 

 near the front end. The teeth are cylindrical ; the hinder ones thick, 

 short, and far apart. Those in the front half of the jaws are very 

 long, subcylindrical, shghtly arched, transversely compressed at the 

 base, that is, more or less flattened on the front and hinder sides by 

 the interlocking of the teeth of the opposite jaws. 



In the older specimens the jaws are compressed at the end ; the 

 teeth are conical, compressed laterally on each side, longitudinal as 

 regards the length of the jaw ; the base is broad, rugulose, and 

 more or less worn away at the upper hinder edge ; the hinder ones 



