478 BALANID.E. 



General Appearance. — Shell conical, ragged, irregular, with the 

 lines of growth plain ; colour dead dirty white. Orifice large, 

 diamond-shaped, narrow towards the carinal end ; notched. Radii 

 narrow, harely distinct from the parietes ; in the same individual 

 sometimes absent, and sometimes forming a mere ribbon, confined 

 to the lower edge of a compartment. The diametric growth is 

 effected by the alse, which seen externally are broad, and strongly 

 marked by lines of growth. Basal diameter of largest recent speci- 

 men 1*15 ; height of highest compartment (a carina) 1*4; and width 

 at base of widest rostrum *85 of an inch. Amongst the fossil speci- 

 mens, height of highest compartment (a carina) 1*8, width of the 

 same one inch ; width of widest rostrum 1*1 of a inch. One of these 

 carinse, a little below the middle point, was actually '3 of an inch in 

 thickness, from which circumstance I have given the generic name of 

 Pachylasma. 



Scuta, triangular, but the width varies a little : growth-ridges pro- 

 minent, sinuous, with a few slight furrows radiating from the apex of 

 the valve. Internally, the articular ridge is not very prominent ; nor 

 is there a deep depression for the adductor muscle, and none for the 

 lateral depressor muscles. The upper part of the valve projects freely. 



Terga, broad, broader than the scuta : the growth-ridges are pro- 

 minent, and angularly upturned close along the scutal margin ; the 

 carinal half of the valve is smooth, with the faintest traces of longi- 

 tudinal striae. A portion of the valve, nearly half of its entire width 

 on the scutal side, is slightly depressed below the general level, and 

 depends slightly beneath the basal margin on the carinal side : this 

 evidently forms the spur. The carinal margin is nearly straight, 

 with the lines of growth upturned along it. Internally, the articular 

 ridge in the upper part is extremely prominent : the crests for the 

 depressor muscles are very prominent, and depend beneath the basal 

 margin like a comb : they extend over nearly half the basal margin, 

 and the muscle, in a corresponding manner, is unusually spread out. 



Structure of Shell and Radii : the compartments are attached to 

 each other less strongly than in any other cirripede which I have ex- 

 amined, so that when dried specimens are soaked in spirits of wine they 

 generally fall to pieces with a touch. In full and half-grown specimens 

 the carino-lateral compartments are nearly as broad as the lateral com- 

 partments ; in very young specimens, about ^th of an inch in basal dia- 

 meter, they are proportionally much narrower. Theivalls are strong even 

 in young specimens ; in old ones they attain a thickness I have scarcely 

 seen equalled except in Chelonobia. Their internal surfaces are smooth, 

 as is the basal internal margin in young specimens, but in old speci- 

 mens it is roughened with short, blunt ridges and little points. The 

 Radii are often absent ; when present they are very narrow, and con- 

 sist merely of a ribbon-like portion, formed by obliquely upturned 

 layers of growth, more prominent than on the parietes. The Alee are 

 very largely developed ; they are added to, during the diametric 

 growth of the shell, in a regular sweep all the way down to the basal 

 margin, and consequently they do not form a rectangular shoulder as 

 is usual ; externally they are plainly marked by lines of growth : they 



