THE SESSILE BARNACLES. 127 



caused by irregularities in the bottom. The vertical portion of the 

 basis has thick walls, copiously porous, the pores small, 0.5 mm. or 

 less in diameter, and crossed by many septa. The cavity of the basis 

 is filled with a mass of cells formed by thin, bubble-like septa which 

 are convex upwardly, often have slender depending pillars, fre- 

 quently' continuous in several or many superposed cells. The upper 

 surface of the cellular mass is irregular, blistered, and hummocky. 



The opercular valves are unknown. 



Length of specimen figured on plate 29, 198 mm. ; diameter about 

 CO mm. 



The specimens figured are from Wild Horse Canyon, Salinas 

 Valley, Monterey County, California, in the San Pablo formation, 

 collected by Homer Hamlin. 



In the same lot, but evidently from another bed, there is a tur- 

 binate, or more exactly, biconic example, filled with hard matrix, 

 figured in plate 28, figure 2. The patelliform basis was evidently 

 attached by the central point only. It is weakly costate radially. 

 The parietes are not ribbed, but their surfaces are irregular. Radii 

 are deeply sunken with abrupt sides. This specimen measures about 

 104 mm. in greatest diameter, the figure being reduced. 



Several detached bases in the lot, one of them figured, plate 28, 

 figures 1, 1&, upper and lower views, are similar externally to the 

 discoidal part of the basis in the t}^pical form, but they show no 

 traces of the attachment of cell walls on the inside. If they belong to 

 the same species, as seems likely, they are from younger individuals 

 which did not yet have the basal cavity filled with a cellular mass. 

 Figure la is natural size. 



SEEIES OF B. AQTJILA. 



BALANUS AQUILA Pilsbry. 



Plate 31, figs. 1, 2, 4a; plate 32, figs. 2-2c. 



1907. Balanus aquila PILSBRY, Bulletin of the Bureau of Fisheries vol. 26, 

 Document No. 617, p. 199, pi. 8, figs. 5-8; pi. 10, fig. 2; pi. 11, fig. 2. 



Type. Cat. No. 32403, U. S. N. M., from Albatross station 4496, 



Distribution. Monterey Bay to San Diego, California. 



The barnacle is large, conic, with a small ovate orifice with toothed 

 margin ; white or grayish white, the lower part covered with a straw 

 or naples yellow epidermis. Opercular valves also partly covered 

 with epidermis. Sheath and interior white. Parietes and basis 

 porous, the radii solid. 



Greatest diameter 72 mm. ; height, 84 mm. Type. 



Greatest diameter 63 mm. ; height, 42 mm. Santa Barbara. 



Greatest diameter 62 mm. ; height 38 mm. San Diego. 



The scutum is narrow; width less than half the length, strongly 

 convex between the occludent and tergal margins, whitish under a 

 light brown or yellowish epidermis. Tergal margin short, not much 



