292 MR. PARKER ON THE COMMON ROCK-LOBSTER. [Mar. 5, 



merits respecting them will possibly he more advantageously published 

 as an appendix to the account of this bird which, as most (though 

 apparently not every one) of our Members are aware, was drawn up 

 more than twelve months ago, at the request of the Royal Society, by 

 Mr. J. W. Clark and Mr. Edward Newton." 



Mr. T. J. Parker exhibited and made remarks upon the stridu- 

 lating organ of the Common Rock-Lobster (Palinurus vulgaris). 

 He stated that the apparatus in question was produced by a peculiar 

 modification of the antennulary sternum and of the basicerite or 

 second joint of the antenna. The antennulary sternum forms a pro- 

 jecting vertical keel, with a rounded anterior border, and slightly 

 convex sides ; the anterior border is grooved in the middle line, the 

 groove being bounded on each side by a strong smooth ridge ; each 

 lateral surface is marked with a shallow groove ; and between this 

 groove and the border, to which it is parallel, the surface is so smooth 

 as to have the texture of polished ivory. The basicerite is uncaleified 

 along a slit-like space on its inner surface ; this space is filled up 

 with a thick chitinous membrane, which is produced superiorly into 

 a large flap, projecting outwards from the surface of the joint. 

 Immediately beneath this flap the chitin becomes thickened, takes 

 on the form of an oval area or pad, about \ inch long by | inch 

 wide, and marked by a number of fine parallel ridges. In relation 

 with the inferior edge of this pad is a small calcified tubercle. 

 When the antenna is in place, the flap works over the ridge on ■ 

 the corresponding side of the anterior border of the antennulary 

 sternum, the tubercle fits into the groove on its lateral surface, and 

 the ridged pad is closely applied to the smooth space between the 

 groove and the border. Under these circumstances, when the 

 antenna is moved upwards the friction of the pad against the smooth 

 surface produces a loud grating noise, the principle being similar to 

 that of the sound produced by the friction of india-rubber against 

 paper. The apparatus can at any time be thrown out of gear, and 

 the antenna moved noiselessly, by slightly abducting the latter. In 

 November last, Mr. Saville Kent remarked in 'Nature' upon the 

 "shrill squeaking sound" emitted by living specimens of Palinurus 

 when handled, this sound being due, according to Mr. Kent, to the 

 friction of the abdominal somites ; and Mr. Parker suggested that 

 the noise referred to may possibly have been produced by the 

 apparatus described. He stated further that the apparatus was 

 possessed by both sexes, although in the two specimens examined 

 the noise produced was far louder in the male ; and he also remarked 

 upon the fact that, notwithstanding the great perfection of the 

 stridulating organ, the auditory organ of Palinurus is in a very 

 imperfect condition. 



The following papers were read : — 



