331) CEYLON PEARL OYSTER REPORT. 



slaty blue-grey colour above and below. The mantle has a number of moderate 

 brownish spots, absent from the centre and extreme margin. The underside of the 

 mantle and foot are finely dotted with brown. The mantle is covered with fine 

 tubercles, somewhat pointed, giving it a slightly pilose appearance ; this is not so 

 marked in the other specimens. The branchiae are 6 in number, compoundly 

 pinnate. The branchial opening is placed far back and has the form of a transverse 

 slit. The jaws are of the usual form, made up of blunt rods ; colour, a pale brownish - 

 straw. Radula with 18 rows, the last two immature, formula 26-0-26, the teeth 

 increasing in size gradually outwards (Plate I., fig. 18), the outermost four teeth 

 again rapidly decreasing (Plate I., fig. 17). 



ABRAHAM'S original specimen of D. labifera came from the Seychelles Islands. 



SUB-FAMILY : PLATYDORIDID^. 



Platydoris inframaculata (Aim.). Plate II., figs. 2 to 7 ; Plate III., figs. 8, 9. 



Amongst the Nudibranchs obtained at Galle is one well-preserved specimen of 

 Platydoris, which is, I think, referable to the above. The general appearance, 

 markings, and tuberculation of the mantle of the type specimen from Amboyna 

 preserved in the British Museum agree fairly well, but it is impossible to decide with 

 certainty upon the identity of closely allied species of Platydoris without an exami- 

 nation of the radula and the usually very characteristic armature of both penis and 

 vagina. 



The ground colour of the Ceylon spirit specimen is pale reddish-brown, the mantle 

 having a few irregular dark rusty markings formed by minute reticulations round the 

 tubercles ; the lower surface of the mantle bears large circular purplish-black blotches, 

 rather larger and fewer than in the type specimen. The mantle is much depressed 

 and covered with minute, close-set, spiculose tubercles. The rhinophore pores are 

 slightly raised. The branchiae are 6 in number, large, 3-pinnate surrounding 

 the long, tubular anus, partially retracted into a wide, deep collar (Plate II., fig. 3). 

 The total length of the animal is 4 '7 centims., width 3 centims., width of foot 

 1 centim. 



The radula consists of 44 rows ; there are 70 lateral teeth on each side and no 

 median tooth. The teeth are simply hooked, increasing in size outwards (Plate II., 

 fig. 4 ; Plate III., figs. 8 and 9). 



The retracted penis (Plate II., figs. 5 and 7) is armed internally with numerous 

 hook-bearing discs, crowded and rather large below, becoming smaller and more 

 distant as it passes upwards, and taking the form of small prickles on the glans. 

 The vaginal wall bears 6 stout, chitinous discs (Plate II., fig. 6) arranged in opposing 

 pairs. These discs are peltate, the boss being formed of 5-6 rounded nodules, 

 and the whole surface being finely granulated. They measure 0'65 millim. in 

 diameter. The size of the largest penial discs is about 0'19 millim. by 0'155 millim. 



