32 bai.anid.*:. 



segment of the mandibles. They are capable of more 

 diversified movements than the other cirri : the anterior 

 ramus is always elongated, with the terminal segments more 

 or less tapering, and is directed beyond (or anteriorly to) 

 the month : the shorter ramus closely resembles in structure 

 the rami of the second pair. In the Chthamalinse the 

 second pair, and in the Balaninae the second and third 

 pairs (as will be more particularly described under these 

 sub-families) differ in structure from the posterior pairs, 

 from which they are separated by a slight interval. The 

 number of segments on the posterior cirri is often great, 

 amounting in Chelonobia even to fifty. Each segment 

 normally is furnished on its inner face, which is usually 

 somewhat protuberant, with from two to rarely eight or ten 

 pairs of long spines or bristles, placed in a double row ; 

 the two spines in the lower pairs stand nearer to each 

 other, and are shorter than the spines in the upper pairs. 

 Between each pair of spines there is either a single, very 

 thin bristle, or often a tuft of such. The pairs are directed 

 somewhat upwards, and they diverge when the cirri are un- 

 curled ; their function is obviously to entangle the prey. 

 On the dorsal or exterior surface of each segment, close to 

 its upper margin, there is a tuft of spines, often composed 

 of thicker and thinner spines ; these, I believe, serve to pre- 

 vent any creature intruding within the sack. On both sides 

 of the upper margin of each segment, there is generally a 

 row of short, blunt, excessively minute spines, which only 

 deserve notice, inasmuch as it is by their increase in number 

 and size, and by the spreading out of the dorsal tufts, and, 

 lastly, by the increase of the little tuft intermediate be- 

 tween the pairs of spines situated in front, that the seg- 

 ments on the two or three anterior pairs of cirri become 

 covered, like brushes, with bristles. The bristles or spines on 

 the second and third cirri are often, especially in Tetraclita, 

 doubly and coarsely pectinated. The bristles on the pedi- 

 cels follow the same arrangement as on the rami; namely, 

 being in regular pairs on the posterior cirri, and crowded 

 thickly, like a brush, on the anterior cirri. The segments 

 in the shorter ramus of the first cirrus, and in both rami of 

 the second, and often of the third cirrus, are broader than 



