THE SESSILE BARNACLES. 79 



Balanus miraMlis Krtiger. Abh. math-pliys. Klasse der K. Bayer. 

 Akad. der Wissensch. (vol. 2, Suppl.-Bd., 8 Abhandlg., 1912, p. 11). 

 Japan. Diameter 20.5 mm.; the walls and opercular valves are very 

 deeply eroded, and therefore no radii are visible. The peculiarly 

 hollowed out tergal border of the scutum is due to erosion of the outer 

 layer of the valve, and will not be present when unworn specimens 

 are found. Affinities uncertain, but I fancy that it will turn out 

 to be a form of B. amphitrite. It is not Balanus perforatus, var. 

 mirabilis Darwin. 



Balanus patdlaris Spengler, Darwin, Monograph (p. 259). 



KEY TO RECENT AMERICAN SPECIES. 



a 1 . Scutum having one to three longitudinal furrows; tergum with a spur-furrow. 



B. Isevis, p. 120. 



a 2 . Scutum having one or several longitudinal rows of pits, and without a distinct 

 adductor ridge; tergum without spur-furrow, the spur broad, short, and truncate. 



B. trigonus, p. 111. 

 a 3 . Scutum distinctly striate longitudinally. 



6 1 . Ribs at inner base of the parietes more numerous than the septa in the wall 



(pi. 35); basis not porous. 



c 1 . Tubes in the parietes without transverse septa. Northern. . B. balanus, p. 149. 

 c 2 . Tubes in the parietes having transverse septa, in the upper half or throughout. 



Northern Pacific B. rostratus, p. 138. 



b 2 . Ribs of the parietes within all continuous with septa in the wall (pi. 40, fig. 4a). 

 c 1 . Adductor ridge of the scutum well developed; tergum with a spur-furrow, 



sometimes closed by infolding of the sides. 



d l . Tergum purple-beaked, with long, narrow spur; pit of the lateral depressor 

 muscle of scutum not bounded by a ridge. A large white, ribbed bar- 

 nacle, often with yellow epidermis; basis nearly solid. California. 



B. aquila, p. 127. 



d 2 . Tergum not beaked; lateral depressor pit of scutum having a raised edge; 

 wall usually pink-striped; basis porous. California to Peru. 



B. concavus pacificus, p. 104. 



c 2 . Adductor ridge of scutum well developed; tergum without spur-furrow, its 

 basal margin hollowed out on the carinal side of the spur; wall white, smooth, 

 with yellow epidermis, the radii wide. Atlantic and Gulf of Mexico. 



B. eburneus, p. 80. 

 c 3 . Adductor ridge of the scutum weak; tergum without a spur-furrow, the spur 



short, truncate distally. 



d 1 . Wall smooth; scutum very strongly striate, latticed; basal margin of tergum 

 not forming an angle with the carinal side of the spur. 



B. spongicola, p. 115. 



(P. Wall ribbed; scutum less strongly sculptured; basal margin of tergum form- 

 ing an angle with the carinal side of the spur. Antilles, Gulf of Mexico. 



B. calidus, p. 118. 

 a 4 . Scutum not striate longitudinally, or very indistinctly so. 



b 1 . Ribs at base of parietes inside more numerous than septa in the wall (pi. 35); 

 basis not porous; beaks of terga project upward far beyond the scuta. 



c 1 . Tubes in the parietea withotit transverse septa B. balanus, p. 149. 



c 2 . Tubes in the parietes having transverse septa in upper part or throughout. 



B. rostratus, p. 138. 



