362 CETACEA. 



made up of fine gritty papillae. Some of these structures also occur on tlie fauces. 

 I have never observed them in 0. brevirostris. They occur in a more scattered con- 

 dition as far back as the posterior wall of the tube of the larynx. Isolated gritty 

 papillae are also distributed over the tube of the larynx and the area immediately 

 posterior to it, and they can be traced some way down the oesoj)hagus. 



Felvic hones mid male organ. — The crura of the penis (Plate XXV^, fig. 3, 

 cc, and cc*) are attached by a strong fibrous connection to the pelvic bones 

 (fig. 3, p and^.* and fig. 4, ap.) which are placed opposite the 15th and 16th lumbar 

 vertebrae (fig. 3, c, t, sp.), and the characters of these bones, their position and 

 variability, are depicted in Plates XXV^, fig. 4, and XLII, fig. 11. The retractor 

 penis, which is highly contractile, lies between the two crura, and at its origin 

 is expanded over the strong fibrous band connecting the two j)elvic bones {pp-^). 

 When pulled out it suddenly contracts to half its extended length. The jjenis 

 is simple and without lobes, and from the base of the prepuce to the tip measures 

 three inches in its quiescent state, but from the way the hinder portion of the 

 organ is doubled on itself, it is evident that when distended with blood it is 

 capable of considerable elongation, probably reaching nine inches in length. The 

 glans or preputial portion is of nearly equal breadth throughout, its transverse 

 exceeding its dorso-ventral diameter, as it is slightly flattened from above down- 

 wards. Its greatest diameter is about three-quarters of an inch. About three- 

 quarters of an inch from its extremity it tapers rapidly to a fine point with a slight 

 intervening swelling, and this portion of the glans with the tip has a remarkable 

 resemblance to the head and snout of a Trionyx. The orifice of the uretlu'a is 

 exceedingly small. The terminal inch constitutes the true glans, and it is coloured 

 like the external skin of the animal, while the portion behind has a pinkish liue. 

 The dorsal surface, unlike any other Cetacean or mammal that I am acquainted with, 

 is marked by a mesial ridge, which begins at the base of the prepuce and extends to 

 the tip of the organ, interrupting the somewhat concentric wavy transverse folds into 

 which this part of the organ is thrown when at rest and which relate to extension. 

 At the base of this long raphe on either side there is a rather large papilla marked 

 at its tip by a patulous orifice, the opening of a gland. I am unable to say whether 

 such a structure exists in the allied species O. brevirostris, as I have had the 

 opportunity to examine only one badly preserved male. 



Skull. — The skull (Plate XLII, figs. 1, 2, and 3) of the purely fluviatile dolphin 

 of the Irawady has so very strong a likeness to that of the round-headed dolphin 

 of the Bay of Bengal and its estuaries, first described by Professor Owen as 

 FJwccena brevirostris,^ that were the skulls the only materials for determinino- 

 the species, considerable dubiety would inevitably be experienced in decidin"' 

 on their specific distinctness. But when the animals are studied as a whole — the 

 only reliable method — other characters gradually unfold themselves, which, when 



' The pelvic bones of thifs species are subject to considerable variation. See Plato XX a, fig. 4, and Plate XLII 

 fig. 11. 



2 Trans. Zoo). Soc, vol. vi , p, 24, pi. iix, figs. 1 to 3. 



