(sect, c), balanus trigonus. 223 



Section c. 



Parietes and basis permeated by pores. Radii not 

 permeated by pores. 



14. Balanus trigonus. PL 3, fig. la — If. 



Parietes ribbed, mottled purplish-red ; orifice broad, 

 trigonal, hardly toothed. Scutum thick, with from one to six 

 longitudinal rows of little pits. Tergum ivithout a longitudinal 

 furrow ; spur truncated, fully one third of width of valve. 



Hub. — Java ; East-Indian Archipelago ; Peru ; West Columbia ; California ; 

 Sidney; New Zealand. Mus. Brit., Cuming, Stutchbury, Dunker, &c. 



General Appearance. — Shell conical, generally depressed ; orifice 

 broad, triangular, almost equilateral ; walls coloured or only mottled 

 with purplish-pink, having either irregularly branching, or regular, 

 longitudinal ribs, which are generally white. The radii are pale pink, 

 or nearly white : the opercular valves have either their upper parts, or 

 nearly their whole surface, clouded with pinkish-purple : the epidermis 

 is not persistent : the walls are moderately strong : the largest spe- 

 cimen was one inch, but generally full-grown specimens are about half 

 an inch in basal diameter. 



The Scuta have the lines of growth highly prominent. From one 

 to five or six rows (7 b, 7 c) of nearly circular, or transversely oblong, 

 deep pits, extend down the middle of the valve ; rarely there is not 

 even one row ; in this latter case, the valve is not striated longi- 

 tudinally. These little pits are caused by one or more deep lon- 

 gitudinal furrows, crossed by the lines, or rather ridges, of growth. 

 In the same group of specimens, I have seen individuals with three, 

 five, and six rows ; and even a few specimens with only one row, or 

 none at all. The outline of the valve is elongated, with the apex 

 slightly reflexed : the inner surface is protuberant, sometimes to a 

 remarkable, but variable degree. The articular ridge is not very pro- 

 minent, but it extends fully half-way down the valve, and generally 

 ends in a small free point. There is a short adductor ridge, and a 

 deep narrow pit or cleft for the lateral-depressor muscle. Terga, ex- 

 ternally smooth, flat, with scarcely a trace of a longitudinal furrow ; 

 spur broad (7 e, If), varying from half to one third of the width of 



