THE ANATOMY OF PLEUROTOMAKIA BEYRICHII. 217 



tion of the fragmentary specimen, tliey have in every case 

 been verified by a comparison with the two complete speci- 

 mens. 



The External Characters. — The first example which 

 came into my hands was the identical specimen whose ex- 

 ternal characters were described by Professor Mitsnkuri in 

 the 'Annotat. Zool./ Japan, vol. i, p. 67; consequently I 

 cannot do better than quote his description in extenso. 



" The animal was not very lively and could not be per- 

 suaded to extend itself fully. At the utmost we were able 

 to see the foot and a part of the head. The sole of the foot 

 was straw-yellow. The side of the foot and the throat were 

 mottled with large and small patches, and streaks of deep 

 carmine-red on the ground colour of reddish yellow. The 

 proboscis was uniformly deep carmine-red. The left tentacle 

 had a small branch near the tip. On the sides and the 

 posterior aspect of the foot we were able to make out two 

 lobes, one standing up from each side of the foot and applied 

 to the shell. It seemed probable to me that when fully 

 extended these lobes enveloped the shell to a greater extent, 

 a supposition which is strengthened, as was first pointed out 

 by Mr. Namiye, by the fact that the shells of Pleuroto- 

 maria hitherto found are all extremely clean, and have 

 never barnacles, worm-tubes, etc., attached to them. The 

 mantle Avas not at all visible, and we were thus not able to 

 see how it is related to the slit on the outer lip." 



It will be seen from the above account that Mitsukuri 

 makes no mention either of the presence or absence of an 

 operculum — a strange omission when we remember that an 

 operculum had been described by Dall as present in both 

 P. Quoyana and P. Adansoniana. When I received the 

 specimen I found that it had no operculum, nor could I 

 find, after a careful examination, any suggestion that. the 

 operculum had been torn away. The only indication of the 

 possible presence of this organ was a minute lobe (fig. 2, 

 op. I.) situated on the dorsal side of the foot in the position 

 of, the opercular lobe of Trochus. The arrival of the 



