THE SESSILE BARNACLES. 201 



BALANUS HOEKIANUS Pilsbry. 



Flute 52, figs. 2 to 2/. 



1911. Balanus hockianus PILSBKY, Bulletin of the Bureau of Fisheries, vol. 

 29, p. 77, fig. 8 (mouth parts and cirri) ; pi. 13, figs. 3-7; pi. in, figs. 

 1, 2. 



* 



Type. No. 38GG6, United States National Museum. 



Type-locality. Albatross Station 4778, Bering Sea, lititude 52 

 12' north, longitude 179 52' east, in 43 fathoms, seated on a gas- 

 tropod shell (Buccinum). 



The shell and opercular plates are white throughout. Shape 

 shorth^ subcylindric, flaring outward at the large triangularly ovate 

 orifice. Compartments solid, without pores; no radii. The pa- 

 rietes are slightly roughened but not distinctly ribbed or sulcate, 

 with no chitinous cuticle and no hairs. The alas are smooth, with 

 extremely oblique upper margins, so that the peritreme is deeply 

 serrate. Internally the compartments have a long glossy sheath 

 below which they are somewhat sulcate, chiefly near the base. 



The rostrum is much the largest plate. Externally, while it is 

 finely, indistinctly rugose longitudinally, there is no distinct cos- 

 tation, and no trace of radii. Inside, the sheath is tripartite. The 

 carina is strongly concave. The lateral plate is wide, triangular, 

 with a well-developed ala but no radius. The carinolateral plate 

 is narrow, recurved, with the ala wider than the parietal area. 

 Inside the sheath is bipartite. 



The basis is an excessively thin transparent film, calcareous at 

 the edges, membranous in the middle. 



Height of the shell 8 mm. ; diameter of the base 8 mm. 



The scutum is moderately thick. It flares outward and is twisted 

 toward the apex. Externally it is indistinctly marked with fine, 

 weak growth-striae and rather widely spaced growth-arrest lines 

 which are scarcely raised. Inside there is a short but well-developed 

 articular ridge, about one- third the greatest length of the plate. 

 The articular furrow is narrow and distinct though not deep. 

 There is no adductor ridge, though a noticeable thickening extends 

 downward from the lower end of the articular ridge, representing 

 a vestigeal adductor ridge. A shallow oblong pit marks the inser- 

 tion of the depressor muscle. 



The tergum is very thick for so small a plate, white, the scutal 

 margin concave, carinal margin short, strongly convex. The spur 

 is long and narrow, separated from the scutal margin by nearly its 

 own width. A smooth depressed band runs to it. The area on the 

 scutal side of this band is marked with widely spaced, strongly 

 arched, linear growth-ridges. The wide area on the other side has 

 very oblique linear growth-ridges, and an interstitial sculpture of 

 very weak, fine, longitudinal striae. There are some minute hairs 



