GENUS VERRUCA. 507 



ever, they are calcareous; and the minute transverse cylinders, 

 of which they appear to be composed, stand further apart, 

 causing the surface of the primordial valve to be marked 

 with little separate circles, instead of by hexagons. 



The shelly matter of which the valves are composed is 

 translucent : it is remarkably destitute of any investing 

 membrane. The under surface is marked with rows of 

 minute approximate pores, parallel to the lines of growth, 

 into which the corium enters : after a portion of shell has been 

 dissolved in acid, these threads of corium are seen to change, 

 a short distance within, into cylinders of yellow chitine, 

 running obliquely through the substance of the valve. 

 These cylinders are about ^ th of an inch in diameter, but 

 in parts they are spindle-shaped and twice as thick : they 

 vary in length, about -^th of an inch being the average 

 length : these cylinders at their upper ends suddenly con- 

 tract into a point, more or less long, or are produced into 

 a very fine tortuous tubulus of chitine, imbedded in the 

 shell : I have seen in no other Cirripedes tubuli of this 

 structure. There are other ordinary tubuli, such as occur 

 in the valves of most Cirripedes, about g^th of an inch 

 in diameter, and which sometimes alternate with the above- 

 described thicker cylinders. There are no external spines. 

 From the number and length of the tubuli of both kinds, 

 the tissue left after the action of acid is singularly com- 

 plicated. 



Basis. — The basal membrane is thin, and is divided, but 

 not very plainly, into concentric slips, marking the successive 

 increments of growth. In the middle of it, in two young 

 specimens, I found with great difficulty the pupal prehensile 

 antennae : they were of small size, measuring from the ex- 

 treme edge of the main or second segment to the end of the 

 disc, only ^ths of an inch : the disc appeared narrow (as in 

 Pollicipes and Scalpellum), with a single spine at the proxi- 

 mate end : the ultimate segment, placed as usual at about 

 right angles to the disc, bore two groups of shorter and longer 

 spines, but I could not count how many. The antennae were 

 enveloped in a mass of cement of a yellow colour, resembling 

 in all its characters the cement of other Cirripedes. In only 

 one case, I believe I saw bifurcating cement- ducts, of extreme 



