REPORT ON THE CRUSTACEA MACRURA. XXxiii 



attached as not to be independent of it ; in many it is fused with it and cannot be 

 demonstrated as distinct. This is the case for instance in Sergestes. One thing, 

 however, is invariably constant, that however few the joints of the peduncle may appear, 

 that which supports the scaphocerite is always the second. 



At the extremity of the peduncle a flagellum is attached which is generally long and 

 slender ; its length varies from half to three or four times that of the animal. Some- 

 times it is short, and in the Scyllaridse it is squamose and discoidal, and in the fossil 

 form Cancrinos claviger, Minister, from the Upper White Jura of Bavaria, it is short, 

 robust, and club-shaped ; but this reduction of length is generally due to the shortness 

 of each articulus. The margins are occasionally armed with a series of more or less 

 important spines, so that in the Palinuridse these organs become effective as a means of 

 protection. As a rule, however, they are smooth and free from hairs or spines, and by 

 their great length sweep the water in search of objects, the character of which they seem 

 to appreciate by the sense of touch. 



In the genus Crangon they are used to assist in concealing the animal beneath the 

 bottom, by playing over the dorsal surface, and drawing particles of sand over the back 

 so that it becomes covered from view. 



In Palinurus they are strong and rigid, being capable of use as weapons of offence 

 or defence. 



The Mandibles. — The mandibles are the appendages attached to the fourth somite, 

 and consist of a large angular joint supporting two or three other joints of rudimentary 

 character, that vary in number and form according to generic distinction. 



The joint of which the mandible proper consists is the hoinotype of the coxa of 

 the crustacean leg, differentiated to fulfil certain specialised functions ; and it possesses 

 very similar characters throughout the whole of the higher orders. It is deeply 

 implanted in the body of the animal by a thin broad process of a concavo-convex form 

 (apophysis), the muscles of which are inserted by strong calcified tendons on the inner 

 anterior margin and at the extremity of the apophysis, the other extremity of the muscles 

 being attached, either to the dorsal surface of the carapace or else to its lateral wall 

 just behind the hepatic tooth. At the points of the mandible opposite to those where 

 the tendons are attached two hinges exist, on which the appendage swings in performing 

 the action of opening and shutting. 



The anterior or distal extremity of the joint is modified to form a grasping or 

 cutting portion and a grinding process ; the former is broad, thin, and of a more or less 

 concavo-convex form, while the latter is stout, cylindrical, and truncate, the truncate 

 extremity being furnished with numerous small teeth and spines of variable form and 

 power. For the sake of clearness of description, I have in this Report named the 

 grasping or cutting portion the psalistoma, on account of its scissor-like mode of 



(ZOOL. CHALL. EXP. PART LII. 1888.) Fife 



