THE SESSILE BARNACLES. 197 



The greater number of lots having widely spaced growth-ridges on 

 the scuta also have smooth parietes; yet this association is not inva- 

 riable. A lot from Port Townsencl, growing on Pecten caurinus^ is 

 as strongly ribbed externally as most hcspcrlus, but in the lower part 

 only, the upper part of the cone being smooth. They reach a basal 

 length of 17 mm. (pi. 49, fig. 2). In another lot from Albatross 

 station 28G9, off northern Washington, there are faint traces of ribs 

 close to the base, thus connecting the strongly ribbed and smooth 

 forms. Some fine groups, growing on Natica, at Albatross station 

 3675, are also transitional in external sculpture (pi. 49, figs. 3, 3<z). 



Figures 1 to I/ are from very regular, smooth, solitary specimens 

 growing on the interior of Pecten. They are not mature, measuring 

 7.25 mm. in greatest diameter, 2.5 mm. high. Other regular, low- 

 conic specimens were dredged by the Albatross in 32 fathoms off the 

 northwestern coast of Washington (station 2869) . The largest meas- 

 ures 13 mm. diameter, 5.8 mm. high, probably about maximum size. 

 Close to the base there are traces of ribs. 



The cylindric form from Puget Sound (pi. 49, fig. 5, on the shell of 

 Thais] is similar to the low-conic form except in shape of the wall. 

 Diameter 11.5, height 8 to 11 mm. ; orifice 9.5 mm. long. 



Californian specimens seen are very small. One of the shortly 

 cylindric form from Albatross station 4457, Monterey Bay, 15 fath- 

 oms, is 7 mm. in greatest diameter. Others from Albatross station 

 4561, Monterey Bay, 15 fathoms, and 3096, off Oregon, in 33 fathoms 

 (pi. 50, figs. 2, 2, 2Z>) are still smaller, the largest 6 mm. in diam- 

 eter; shape conic with large orifice, or cylindric, the orifice as large 

 as the base ; radii inore oblique than in the usual B. hesperius. Scutum 

 having very low, widely spaced growth-ridges, and internally sim- 

 pler than ordinary hesperius the callus between articular ridge and 

 adductor pit smooth, raised into an acute ridge along the pit. 



Most of the characters are those of young hesperius., but the appear- 

 ance of the specimens, which are very numerous, is that of adult 

 barnacles. Possibly a small race inhabits the coast from Oregon to 

 Monterey Bay, but further shore collections are needed to demon- 

 strate this. Both lots grew on twigs. 



In Alaska the smooth form with convexly conic shape has been 

 taken at Sitka ; diameter 15.5 mm., height 7 mm., growing on 

 Tegula, pulligo (pi. 49, fig. 4). Further north, in the waters where 

 typical B. hesperius is abundant, the variety Iwvidomus seems to be 

 rare. There are a few specimens up to diameter 6 mm., from Chag- 

 afka Cove, Kodiak, and from the mouth of Port Clarence, which, by 

 the smooth exterior and low, widely spaced growth-ridges of the 

 scuta, seem to belong here. Both grew on small gastropods. Smooth 

 individuals seen from other Alaskan localities may be, at least in 

 part, immature stages of the ribbed B. hesperius. 

 4729 Bull. 9316 14 



