336 GENUS — LITHOTRYA. 



veloping membrane, with its spines, is present in all the 

 species of the genus ; in L. Rhodiopus these spines are 

 much larger than in L. dorsal is, and on the inner sides 

 of the carina they are trifid and quadrifid, and large 

 enough to be conspicuous with a lens of weak power. 



Pedimcle. — The most remarkable fact concerning this 

 part, is that the outer tunic, together with the calcareous 

 scales with which it is covered, is moulted at each 

 successive period of exuviation and growth. I demon- 

 strated this fact in L. dor sails and L. trimcata, by removing 

 the old tunic and finding a new membrane with perfect 

 calcified scales beneath ; and as these two species, (I ob- 

 tained, also, pretty good evidence in L. Nicobarica,) are 

 at the opposite extremes of the genus, no doubt this fact 

 is common to the whole genus. I know of no other 

 instance, amongst Cirripedia, in which calcified valves or 

 scales are moulted. I am not certain that the whole skin 

 of the peduncle is thrown off in a single piece ; though 

 this almost certainly is the case with the uppermost and 

 lowest portions. The animal's body is partly lodged 

 within the peduncle, which is generally from one to three 

 times as long as the capitulum, and in the upper part is 

 fully as broad as it. The scales with which it is clothed, 

 extend up in the triangular interspaces between the basal 

 margins of the valves. The scales of the upper whorl, or 

 of the two or three upper whorls (PL VIII, figs. 1 b' 

 and 3d) are larger than those below; and these latter 

 rapidly decrease in size, so as to become low down on the 

 peduncle, almost or quite invisible to the naked eye. The 

 scales in each whorl, are placed alternately with those in 

 the whorls, above and below. All the upper scales are 

 packed rather closely together; those in the uppermost 

 row are generally nearly quadrilateral ; those in the few 

 next succeeding whorls, are triangular, with their basal 

 margins protuberant and arched ; the scales, low down 

 on the peduncle, stand some way apart from each other, 

 and generally consist of simple rounded calcareous beads, 

 of which some of the smallest in L. dorsalis were only 



