(sect, e), balanus cariosus. 273 



the older ones on the same stones, I am of opinion that the term of life 

 of the species is two years. Of the older shells, which I examined and 

 found living in the spring, nine tenths are now dead, the walls only 

 remaining, the opercular valves having been washed away." 



Mr. Thompson goes on to say, that the individuals which 

 had, on July 3, a basal diameter of from two and a half to 

 three lines, had attained, by the 30th of September, a dia- 

 meter of four and a half lines, this being here the maximum 

 size of the species. 



30. Balanus cariosus. PL 7, fig. 3 a — 3 e, 



Lepas cariosa. Pallas. Nova Acta Acad. Scient. Petrop. torn, ii 



(1788), p. 240, Tab. 6, fig. 24. 



Parietes thick, formed by several roivs of unequal-sized 

 pores. Tergum narrow, with the apex beaked, and spur 

 sharply pointed. 



llab. — Columbia River, west coast of North America, Mus. Brit, and 

 Cuming; Behring Straits (Capt. Kellett) ; the Kurile Islands, according to 

 Pallas. Attached to shells, and to each other in groups. 



General Appearance. — Shell steeply conical, with a rather small 

 oval orifice ; or cylindrical, with a large rhoraboidal and little toothed 

 orifice. Colour dirty white. Surface either simply rugged, or more 

 commonly covered by numerous, narrow, extremely prominent, longi- 

 tudinal plaits ; from the manner in which these overlap each other, the 

 shell almost appears as if thatched with straw. The upper corroded 

 part of the shell usually exhibits a cancellated and finely punctured 

 surface. The radii are generally very narrow, forming towards the 

 base of the shell a mere narrow ribbon to each compartment, and 

 often hardly distinguishable ; but in one specimen they were of con- 

 siderable width : in the former case, the alee are often widely exposed. 

 The largest specimen which I have seen was 1*5 of an inch in basal 

 diameter, but Pallas gives 22 as the measurement of a specimen from 

 the Kurile Islands. 



The opercular valves are united to each other and to the shell by 

 unusually strong membrane ; and the upper parts of both valves, in all 

 the specimens seen by me, have been much disintegrated. The Scutum, 

 in old specimens, is faintly striated longitudinally, but in some there is 

 hardly a trace of this : the occludent margin is furnished with a few 

 large knobs, not corresponding with every alternate line of growth (as 

 is usual with other species), but with every fourth or fifth line. Inter- 

 nally, the articular ridge is moderately prominent (in young specimens 

 more prominent) and reflexed. The adductor ridge is sharp and 



18 



