3IO CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



ascribed to it by the earlier writers have vanished, and its 

 close relationship to Corella has been ascertained. But there 

 are still several important points in its structure that remain 

 to be elucidated. Kiaer (1893 and 1896) cites all the 

 important literature dealing with the species. C. production, 

 the only other species J of the genus, was described by 

 Stimpson (1864) from specimens collected at Puget Sound; 

 and his very incomplete account was supplemented in 1884 

 by Drasche's (1884) excellent description of a few individ- 

 uals from the same locality. So far as I know this species 

 has not been described since that time. 



Range and External Appearance. 



C. productum undoubtedly occurs all along the Pacific 

 coast of the United States and probably also of British 

 Columbia. The center of its range seems to be in the 

 vicinity of Puget Sound, for the specimens from there are 

 quite numerous and surpass in size any that I have met 

 with in California. In the latter state it has been collected 

 from Point Mendocino in the north to San Pedro in the 

 south, but is nowhere abundant. A few specimens were 

 found on the under sides of rocks, some were obtained by 

 dredging in shallow water, and a few from 80 or 90 

 fathoms. 



The color in the younger individuals is whitish, the test 

 being transparent so that the internal organs can be seen 

 through it. In most of the older individuals, however, the 

 surface is conspicuously coated with an opaque yellow or 

 brownish layer which will be considered more in detail 

 later. Some individuals have the base of the test wrinkled 

 and discolored, while the remaining portion is thin and 

 quite clear. 



The shape is very characteristic, in spite of considerable 

 variation, dependent largely upon the age of the individual 

 (figs. 1, 2, 2a). The most striking external feature is the 

 oval disk which is divided into the movable plates that have 



1 Neither Stimpson's (1R52) description of Asciditt geometrka nor the figure published by 

 Verrill (1874) show that the individuals they examined differ iu the least from C. 

 jnacleayamtm . 



