LAGENOEHTNCHUS. 579 



Colour. Dark slaty blue, nearly black, above, and but little paler 

 below. 



Dimensions. Total length about 7 feet. Snout to dorsal fin 

 46 inches, height of dorsal 3'75, snout to pectoral 16'5, anterior 

 margin of pectoral 17, breadth of pectoral 6'20, expanse of caudal 

 fin 21-5. A skull measures 10'6 in basal length, 7*4 broad across 

 orbits, length of rostrum 5*1. 



Distribution. Bay of Bengal, ascending rivers as far as the tide 

 extends ; also found at Singapore and in North Borneo. 



385. Orcella fluminalis. The Irrawaddy Porpoise. 



Orcella fluminalis, Anderson, P. Z. 8, 1871, p. 143, fig. 2 ; id. An. 

 Zool. Res. p. 358, pis. xxv a, xxvii, &c. ; Blyth, Mam. Birds Surma, 

 p. 34 ; True, Delphinida, p. 182 ; W. Sclater, Cat. p. 319. 



Form very similar to that of 0. brevirostris. The dorsal fin is 

 situated somewhat farther back, and is smaller, lower, and less 

 falcate, and the pectorals are rather shorter and broader. The 

 head is less globose. Teeth about ^. 



Colour. Pale slaty above, whitish below, numerous narrow 

 streaks irregularly dispersed on the sides. 



Dimensions. Length of a male 7| feet, snout to dorsal fin 55 

 inches, to pectoral 17, length of pectoral along anterior margin 17. 

 Basal length of a skull 10-3 inches, breadth between orbits 7, 

 length of rostrum 4-6. In another male 86 inches long, the 

 dorsal fin was a little over 2 high. 



Distribution. The deeper channels of the Irrawaddy from below 

 Prome to above Bharno. This porpoise has not been observed in 

 the tidal waters of the river delta. 



Habits. The Irrawaddy porpoise is gregarious, soh'tary individuals 

 being rare, and it keeps to deep water, rising to breathe every 

 minute or two as a rule, and emitting " the short blowing sound, 

 which ends in the more feeble one of inspiration " (Anderson). 

 The food, so far as known, is exclusively fish. 



Mr. Thomas has recently united this species with 0. brevirostris, 

 but the absence of that form in other Indian rivers renders it 

 probable that 0. fluminalis is really distinct. 



Genus LAGENOBHYNCHUS, Gray (1846). 



Head with a short, not very distinct beak, or pointed, without a 

 beak. Dorsal and pectoral fins moderate. Caudal ridges very 

 prominent. 



Teeth variable in size. Rostrum flat, not greatly exceeding the 

 remainder of the skull in length. Premaxillse flat or slightly 

 convex above. Pterygoids usually in contact. Maudibular sym- 

 physis short. Vertebrae very numerous, 73 to 92 (generally 

 over 80). 



