REPORT ON THE CRUSTACEA MACRURA. XXV 



are really external, and that these only could receive tactile impressions, since the other 

 parts are covered by the eyes, the rostrum, squame of the antennae, and the antennule 

 of the opposite side. The fringing setse along the margins of the surface which bears 

 the opening of the auditory sac, as well as the close-set row of fringing setse which 

 cover the opening, act, doubtless, as strainers, and prevent the entrance of foreign bodies 

 to that delicate organ." 



Among the Dendrobranchiata the characteristic features of the first antennae remain 

 the same ; that is, the peduncle consists of the same number of joints, and terminates 

 in two slender flagella. But the first joint, instead of being cylindrical, is broad, flat, and 

 deeply excavate on the upper surface for the reception of the ophthalmopod, which when 

 at rest lies ensconced and protected by a fringe of hairs (the blepharis) that surrounds 

 the excavation. In the genus Sicyonia the excavation is so deep that its floor becomes 

 translucent. But whenever this is the case, the inner and outer margins become 

 correspondingly thick and strong, the outer margin being armed with a long pointed 

 process (stylocerite), often of considerable strength, and the inner margin with a long, 

 slender, unjointed appendage, which I have named the prosartema, and which is 

 confined to the genera of this division, and is not unfrequently reduced to a rudimentary 

 and obsolete condition. 



In Pen&us canaliculatus the prosartema exists in the most perfectly developed 

 form; it arises from the inner marginal wall near the base, and projecting forwards, 

 overbes the ophthalmopod when the latter is at rest ; the margins are fringed with 

 hairs, and it reaches quite to the extremity of the first joint (PI. XXXI. fig. b). 



In Penasus serratus the prosartema is scarcely as long as in Penseus canaliculatus, 

 the margins are fringed with hairs, and the stylocerite on the outer side is short and 



pointed. 



In Sicyonia carinata (PI. XLIII. fig. 3b) the prosartema is reduced to a rudimentary 

 lobe thickly surmounted with hairs, and the stylocerite on the outer margin is long, 

 slender, and pointed. 



In the genus Aristeus the prosartema is little more than a rudimentary process 

 fringed with hairs, and the stylocerite is produced to a length that passes beyond the 

 distal extremity of the second joint of the peduncle. 



Both these structures are useful for the protection of the ophthalmopod. The 

 stylocerite does not exist in the Trichobranchiata, and only in a reduced condition in 

 the genus Sergestes ; while both it and the prosartema are absent in Lucifer. 



In this division the second and third joints of the peduncle are shorter and stouter 

 than the first; in many cases they assume a subcylindrical form, and they are 

 occasionally armed by having the distal angles produced into teeth ; but in all essential 

 points these two joints are only of importance as being the supporters of the two 

 flagella. In the genus Penseus the flagella are never extremely long, and are sometimes 



(ZOOL. CHALL. EXP. — PART LII. 1888.) 'if d 



