(sect, b), balanus calceolus. 219 



Norway ; but I do not believe that it is the same with our 

 present species. 



General Appearance. — The degree of elongation of the shell in its 

 rostro-carinal axis varies considerably (3 a, 3 b) : the elongation is due 

 to the production of the rostrum and of the corresponding end of the 

 basal cup. These two portions of the shell always form together an 

 angle, and sometimes an acute angle, whereas in all the many specimens 

 which I have seen, the carina and the carinal end (or heel) of the basis 

 together form a straight line ; yet I should not be surprised if this end 

 of the shell was sometimes produced. The surface of the shell is 

 smooth, or sometimes marked with very minute projecting points : it is 

 almost always covered by the horny bark of the Gorgonia. The colour 

 is either dull purplish-red or dull purple, with obscure longitudinal 

 stripes, and often more or less transversely banded with white. The 

 rostrum is either white or very feebly tinted, being always paler than 

 the rest of the shell : the radii are usually paler than the parietes, and 

 are sometimes white : the carinal end of the basal cup is tinted of the 

 same colour with, but rather paler than, the compartments. The orifice 

 is rather small compared to the shell, and nearly heart-shaped. The 

 carino-lateral compartments are about one-third of the width of the 

 lateral compartments. The shell is very strong, and the sutures resist 

 the action of boiling caustic potash. The largest specimen which I 

 have seen was '7 of an inch in extreme length, and under *25 in ex- 

 treme breadth. 



Structure of the shell and basis. — The parietes are permeated by 

 quite distinct pores, — a character sufficient by itself to separate this 

 from the following species ; the longitudinal septa forming the tubes 

 are slightly denticulated at their bases. The radii have their summits 

 quite square, extending from apex to apex of the adjoining compart- 

 ments. The alse have oblique summits. The sutural edges of the 

 radii have approximate septa, which are obscurely denticulated : the 

 interspaces are filled up solidly, so that the radii are not porose. The 

 basis is distinctly porose, by which this species can be distinguished 

 from B. navicula and cymbiformis. The basis has a deep furrow on 

 the under side, from clasping the thin horny axis of the Gorgonia : the 

 basal point of the rostrum is also notched from the same cause, and, 

 as a consequence, its upper surface becomes slightly furrowed along its 

 whole length. 



The Scuta have an articular rrdge but moderately prominent, and 

 only slightly reflexed ; the basi-tergal corner is rounded off; there is 

 no adductor ridge ; there is a small, rather deep, distinct pit for the 

 lateral depressor muscle. Terya ; externally the surface is considerably 

 depressed in the line of the spur. The spur is between half and one- 

 third of the width of the valve : its lower end is square and truncated, 

 or in some degree rounded ; it is sometimes (3 e) dentated with a few, 

 minute, sharp teeth. The articular ridge is but slightly developed ; 

 the crests for the depressor muscle are very feeble. 



AnimaVs body unknown. 



