No. 2362. BARNACLES OF THE SAN JUAN ISLANDS— PILSBRY 115 



adductor ridge, and not longitudinally striate externally. In Bal- 

 anus crenatus the walls are conspicuously porose, and the scutum is 

 not distinctly striate longitudinally. All of these species are of about 

 the same size. While all occur on the San Juan Islands, they are not 

 associated in any of the groups at hand, each forming its own colonies 

 on separate objects. The specimens of B. engbergi were found 

 on a board which had floated in. To what extent, if any, these species 

 inhabit different zones in the San Juan Islands remains to be ascer- 

 tained. In southern California B. glandula occurs at and above low 

 tide. B. crenatus, on the eastern coast, is found below low tide. 



EXPLANATION OF PLATE 20. 



Fig. 1, 2. Mitella polymeries (Sowerby). Olga. Natural size. 



3. Balanus cariosus (Pallas). Friday Harbor. Slender individual from 



a close group. Natural size. 



4, 5. Balanus engbergi new species. Olga. Top of the type and lateral 



view of two paratypes. X3. 

 6. Balanus cariosus (Pallas). Friday Harbor. Part of a compact group. 

 Natural size. 



