144 BULLETIN 93^ UNITED STATES NATIONAL MUSEUM. 



24: mm. high. The scutum is deeply striated longitudinally, just as in 

 B. T, apertus^ and all the opercular valves are faintly tinged with 

 pink toward the apices. The parietal tubes are small and numerous, 

 36 in the rostrum of one individual. 



BALANUS ROSTRATUS APERTUS Pilsbry. 



Plate 36, fiRS. 3-6; pL 37, figs. 1-lc. 



1911. Balanits rostratus apcrtus Pilsbry, BulL Bur. Fisheries, vol. 20, p. 

 74, fig. 6, pi. 12, fig. 4, 7; pi. 13, fig. 1, 2, 8, 9 (issued Feb. 17). 



Type.— No. 38G67, U.S.N.M., from Albatross Station No. 4778, 

 Bei-ing Sea, north latitude 52° 12', east longitude 179° 52' in 43 

 fathoms ; embedded in a sponge. 



Distribution. — Bering Sea. 



The shell is white under a very thin marguerite-^^ellow epidemis, 

 often deciduous ; subcylindric or conic, with a large, triangular-ovate 

 orifice, frequently almost or quite as large as the base. The parietes 

 are marked with minute growth-strise, usually showing lines of 

 minute granules at considerable intervals ; there are some irregulari- 

 ties but rarely any ribs, some specimens (including the type) bearing 

 a few short, acute spines projecting downward, each terminating 

 a short rib. The radii are much wider than in B. rostratus, with 

 the upper edges parallel to the base. They are only very little 

 sunken beloAv the parietes. Internally the parietesi are deeply, 

 closely, and sharply ribbed. Parietal tubes square, crossed l)y many 

 transverse septa in the upper part, but without septa near tlie base. 

 The tubes are more numerous than in B. rostratus, about 18 (16 to 

 over 20) in the rostrum. The wall is thin in the typical form, the 

 tubes therefore compressed. 



Opercular vah^es as in B. rostratus except that the tergum (pi. 

 37, figs, la, Ir) is narrower, and often has well-developed crests for 

 the depressor muscles. The terga of both forms are drawn in 

 figure 39. 



The basis is concave, often deeply so, in specimens growing on 

 sponges, the typical station of the subspecies. It is rather thin, with- 

 out pores. 



Height 46 mm., greatest diameter 33 mm., length of aperture 19 

 mm., length of tergum 22 mm. (Station 4778). 



Height 45 mm., greatest diameter 31 mm., diameter of base 24 

 mm., length of aperture 26 mm. (Station 4778). 



Height 27 mm., greatest diameter 26 mm. (Captains Harbor). 



Height 44 mm., greatest diameter 31 mm. (Unalaska). 



Height 33 mm., greatest diameter 21 mm., length aperture 29 mm. 

 (Station 2849, on Terehratiilina) . 



