OPISTHOBRANCHIATE MOLLUSCA. 359 



The male gonads (Plate VI., fig. 17) agree fairly closely with PLATE'S description. 

 The penis rod is long and slender, the glans short and closely covered with minute 

 hooks about 0'04 millim. in length. 



The length of the "cartilaginous" rod is 16 millims., that of the spinulose glans 

 1*8 millims. The dart sac with its ampulla is of the usual form, the ampulla long 

 and rather narrow and sharply curved at its anterior end, where it overlies the 

 oesophagus. The length of the ampulla is 10 millims., the distance from the ampulla 

 to the papilla of the dart sac 8 millims. The dart (Plate VI., fig. 13) is straight, 

 regularly tapered ; length 2 '8 millims. Its free extremity shows a slight curve and 

 has a solid lateral lip. 



The radula (Plate VI., figs. 19 to 22) is of a pale yellow colour very slightly 

 chitinised. It is made up of 60 rows of 83-1-83 teeth of the usual form. The 

 central tooth is slightly broader than long ; the lateral teeth, except those close to the 

 middle line, are produced downwards into a broad adze-shaped hook and upwards 

 into an irregular thin tongue, which takes part in their attachment to the radula 

 ribbon. 



The contents of the stomach consisted of quartz sand grains and a quantity of 

 white flocculent matter, amongst which a few Foraminifera were noticed. 



Onchidium verruculatum is very widely distributed in the Indian and Pacific 

 Oceans, occurring from the East Coast of Africa and the Red Sea to Japan and 

 Australia. 



FAMILY: MAKSENIAD^E. 



Marsenia perspicua (LiNN.) Plate VI., figs. 23 to 26. 



There are eleven specimens of Marsenia in the collection, most of them from 

 Cheval Paar and its neighbourhood and the remainder from South-east Modragam, 

 Gulf of Manaar. and Galle. Externally they are not to be distinguished from the 

 common M. perspicua of European waters, with which species also the radula 

 (Plate VI., figs. 24 to 26) and shell are in close agreement. The largest specimen, 

 one of those from South-east Modragam, is a female, and measures 2 '5 centims. by 

 2 '2 centims., the shell (Plate VI., fig. 23) measuring 1'6 centims by 1'2 centims. 

 These measurements are somewhat in excess of those usually attained by European 

 specimens, but the difference in size and locality does not seem to warrant the use of 

 a separate specific name. 



