180 Puget Sound Marine Sta. Pub. Vol. 1, No. 16 



The specimens from the north side of Brown Island^ locality No, 3, 

 were rock-sheltered forms. They were further protected by a growth of 

 Fucus or seaweed. The individuals here were subjected to the force of 

 the waves to some extent, but not as much as were those at Turn Island. 



The specimens from 35 and 50 fathoms, localities No. 4 and No. 5, 

 from the channel northeast of Brown Island, were subjected to wave and 

 current action varying in degree with their depth. 



The specimens from locality No. 6, from 80 to 90 fathoms in the 

 San Juan Channel, are from comparatively quiet water, the normal con- 

 dition for the best brachiopod habitat. 



The specimens from locality No. 7, from 10 to 80 fathoms, were taken 

 by a continuous drag across San Juan Channel from a point half a mile 

 south of Point Caution, on San Juan Island, thru 90 fathoms in the mid- 

 dle of the channel up to 20 fathoms near Point George on Shaw Island. 

 It is thus a mixture of the specimens exposed to the action of the waves 

 and currents and of those from the comparatively quiet waters of the 

 deeper portions of the channel. 



Turn Rock, locality No. 8, is a rock projecting above the low tide 

 line at about one-sixteenth of a mile east of Turn Island. It is completely 

 covered at the highest tides. Three specimens were obtained from this 

 place, two from sheltered crevices, the other exposed to the waves and cur- 

 lents. 



The embryonic brachiopods pass thru a free-swimming stage which 

 lasts for several days. During this time they are carried about by the 

 waves and currents and are thus introduced into all habitats. The young 

 of the shallow water forms and the young of the deeper water forms are 

 thoroughly mixed. At the proper stage of development the animal at- 

 taches itself to some foreign object, becomes sessile, and begins to develop 

 the shell or protegulum. 



The specimens in the young shell stage, including all from 2.5 to 5 

 mm. in width, were carefully measured to find if there was any variation 

 in the shell form which might have been inherited. No variation could 

 be detected in the specimens from the same habitat or in those from 

 different habitats. 



In the older stages, including all specimens over 5 mm. in width, 

 the shells varied with the conditions under which they grew, from wide 

 spirifer-like to round, almost smooth forms, the extremes being in the 

 mature individuals {Figs. 1-4, plate 32). 



The marked tendencies of the variation seemed to be a shortening 

 of the shell and a rounding of the anterior angle. These characters were 



