THE SESSILE BARNACLES. 



211 



especially along the alcT, there is often an acute ridge, sometimes over- 

 hanging, or a strong longitudinal rib. The strong, calcareous basis 

 is flat or irregular, and never forms part of the wall. 



The scutum is flat, with well-developed growth-ridges; faint, ir- 

 regular and rather close longitucTinal scratches may be seen between 

 the ridges. The articular ridge is very low, narrowly reflexed, its 

 contour gently rounded from end to end; it is confluent with the 

 adductor ridge, which is represented by a low callous, rounded or 

 angular along the depressor muscle scar. 



The tergum is more delicately ridged than the scutum, and there 

 may be a few weak longitudinal striae near the sides. The furrow is 



Fiu. 07. 



-Balanus evermannIj one-half natuual size, a, NEAK Bering Island, 

 SiMUSHiK Island, No. 38G02. 



b, NEAR 



deep and narrow, the sides partly folded in. The spur is narrow, 

 separated from the basiscutal angle by twice its own width. Articu- 

 lar ridge moderate. There are small crests for the lateral depressor 

 muscles. 



The compartments are strong, rather thick, but very weakly ce- 

 mented together. The carina is recurved, but the other compartments 

 usually curve inward at the orifice. The parietes of the carinolaterals 

 are always very narrow — less than half as wide as those of the laterals. 

 The radii are wide or moderate, Avith very long, steeply sloping, smooth 

 summits; sutural edges not denticulate. The ala; are extremely 

 wide, summits strongly oblique ; their surfaces are smooth and nude, 

 except for the distal triangles, which often retain the epidermis; 

 edge without septa or denticles. The sheath is glossy above, its 

 lower edge hanging close to the wall, leaving narrow cavities. Be- 

 low it the parietes are almost smooth, except close to the base, where 

 they become very closely and acutely ribbed, the ribs flattened and 



