14 INVERTEBRATA OF MASSACHUSETTS. 



angles grooved lengthwise, so as to form numerous unequal, irreg- 

 ular ribs ; and these are crossed by distant, circular threads, 

 which probably indicate the stages of growth ; the depressed 

 areas are plain and glistening, marked across by regular, deeply 

 sculptured lines. Aperture sub-triangular. Two anterior valves 

 of the operculum deeply grooved or plaited ; the two posterior, 

 on each side, rising considerably above them and curving forwards, 

 resemble the beak of a bird of prey ; at their sides slightly 

 grooved. Diameter at base 1 inch ; height 1| inches. 



This species probably does not breed in our climate, but is one 

 of the most common shells found on vessels arriving from warmer 

 regions. 



There are some other species, similar to this, which are occasional- 

 ly, but less frequently, observed. B. tiilipa is principally distinguished 

 by its more rosy tint ; the raised areas are distinctly marked across, 

 but scarcely at all lengthwise, and the depressed areas are nearly 

 smooth. B. gigas and sulcuta are also closely allied. 



BALAPfUS GENICULATUS. 



Shell conical., tvhite, the prominent triangles icith 8 or 10 usually 

 alternately larger and smaller ribs, rendered rough by coarse lines 

 of groioth ; valves of operculum coarsely striated. 



Figure 9. 



State Coll., No. 254. Soc. Cab., No. 2310. 



Balanus geniculatus, Conrad; Journ. Acad. JVat, Sc, vi. 2G5, pi. 11, f. IG. 



Shell regularly conical, dirty greenish-white ; much like B. tin- 

 tinnabulum in its exterior, but broader at base in proportion to 

 its height, and never inflated ; the elevated triangles on each 

 side of the posterior one are very small, with only two or three 

 ribs ; the others are sub-equal, and have 8 or 10 ribs ; these 

 are much raised, but usually alternately larger and smaller, 

 somewhat compressed at the sides, and their edges rendered 

 nodulous by the conspicuous, rather distant lines of growth, which 

 cross them. The depressed areas are faintly marked with minute, 

 crowded cross lines. Diameter of the aperture about half that 

 of the base. Operculum having the anterior valves wrought into 

 coarsely plaited ridges, which incline over each other, and which 



