134 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



The young barnacle, sometimes up to a diameter of 25 mm. or more, 

 is more or less strongly ribbed (pi. 30, fig. 2a, Puget Sound) ; but old 

 ones, by wear of the summit, lose this sculpture wholly or to a great 

 extent. Plate 30, figure la, Straits of de Fuca, shows about the maxi- 

 mum size of specimens preserving the external surface unworn. 

 Earely a diameter of GO mm. is attained before the walls become worn. 

 Some specimens of B. nubilis, Avhen young, imitate B. rostratus super- 

 ficially, having abruptly sunken radii and a similar shape and habit 

 of growth. 



Large individuals, such as are common in Puget Sound, are as a 

 rule deeply eroded, showing the crowded, thin-walled parietal tubes, 

 which are seen to have but few transverse septa. These old specimens 

 are often riddled by boring animals, so that all external characters 

 of a barnacle are lost. The orifice is usually A^ery ample, and the 

 sheath rather short, the wall always hollow below it (pi. 30, fig. 4, 

 four-fifths natural size). 



Young specimens are deeply ribbed inside the parieties. The flat 

 basis is thin and poreless in the middle, but thicker, with numerous 

 I^ores, toward the periphery. Old ones become entirely smooth in- 

 side and usually have a deep, pocketlike basis. In one group from 

 Port Orford, Oregon, the base is very dee^), the total length 152 mm., 

 of which the compartments form only one-third or less; diameter, 

 75 to 100 mm. The gi-eatest diameter is around the junction of basis 

 and wall. A more usual size is, height, 85 mm.; greatest diameter, 

 80 mm. (near Port Townsend). A very low individual from Puget 

 Sound measures, height, 55 mm.; greatest diameter, 100 mm. The 

 basis in this example is nearly flat. Another large example measures, 

 height, 105 mm.; rostrocarinal diameter, 103 mm.; length of ori- 

 fice, 64 mm. 



To increase the capacity by deepening of the basis is imusual 

 among the species most nearly related to B. mibilis. Some other 

 species, such as B. crenatus, become elongated by lengthening of the 

 compartments. The serried spinules, standing in saw-tooth like row 

 along the posterior sutures of the segments of the last three pairs 

 of cirri are a very characteristic feature of B. nuMlis, but B. aquila 

 has almost exactly the same structure. In B. fos, which is otherwise 

 closely related, this arrangement of spinules is seen only in an in- 

 cipient stage. 



B. nuhilw lives on rough, rocky or shelly bottoms in water of no 

 great depth, but probably always well beloAv Ioav tide. The greatest 

 depth recorded is 37 fathoms. It was not taken in deep water off 

 the California coast by the Alhatross, and probably does not exist 

 much below the depth mentioned. Santa Cruz is probably at or 

 near its extreme southern range, and it can hardly be expected much 

 farther north than the southern bomidary of Alaska. The extensive 



