CIRRIPEDES. MOLLUSCA. BALANUS. 15 



are crossed by very fine radiating lines. Diameter at base 1 to 

 1| inches, height two thirds of the diameter. 



Found ahnost invariably attached to Peclen J\Iagellamcus, on 

 which it is occasionally drawn up by our fishermen ; and is abun- 

 dant along the eastern coast of Maine, and at the Bank fishing- 

 grounds. 



This shell, like its co-species, is subject to many varieties ; and 

 some of them approach so nearly to some of the figures and descrip- 

 tions of B. Scoficus and B. communis of the North of Europe, that it is 

 really difficult to decide upon its title to a distinct appellation. In this 

 case it seems proper, for the present, to retain the name which Mr. 

 Conrad undoubtedly applied to this shell. The number of ribs varies, 

 as do the elevations upon them ; which last are usually two, however, 

 as Mr. Conrad observes. 



Balanus eburneus. 



Shell ichite^ smooth, obliquely conical, the raised triangles with 

 lanceolate points, all inclined backicards, icithin regularly grooved ; 

 operculum loith the two anterior valves decussated at base, not 

 beaked. 



Figure 6. 



State Coll., No. 253. Soc. Cab., No. 3418. 



Shell white, smooth, hinge obliquely conical, circular at base, 

 inclining backwards ; the raised portions are smooth, or very 

 faintly wrinkled lengthwise ; they all terminate in sharp, lance- 

 pointed summits, all of which point backwards, and the last one 

 curves over so much as to form a prominent beak. The interme- 

 diate, depressed spaces are small and usually plain, but in very 

 old specimens they are crossed by crowded, rasp-like lines. In- 

 terior regularly and firmly grooved up and down, and the walls 

 with a single series of pores, equal in number to the grooves. 

 Aperture constantly ovate-triangular, rounded in front, acutely 

 angular behind, moderately large. Operculum has the two 

 anterior valves checked with transverse and longitudinal hnes, 

 which are well defined at base, but almost disappear at tip ; they 

 are coarsely toothed at their adjacent edges ; the posterior valves 

 very slightly grooved across. The tips of all four valves meet 

 and form an accurate pyramidal summit. Diameter at base * 

 inch, height | inch. 



