54 



The shoreline of Brown Island is very irregular, and is bro- 

 ken into a number of niches isolated by narrow stretches of 

 gravelly or muddy beach. As a result of this partial isolation 

 we have in this area a number of closely related populations 

 differing mainly in size, but with minor deviations in colora- 

 tion and sculpture. Eight of these niches have been noted. The 

 specimens figured in Plate xxiv were derived from a popula- 

 tion inhabiting a protected cove in which favorable conditions 

 prevailed, and as a result we find shells of a somewhat larger 

 size than those of a similar type of sculpture and lack of pig- 

 mentation found at Point Caution, a short distance away, 

 as shown in Plate xxv, where unfavorable growth conditions 

 are present. 



In this morph there is greater variation in sculpture than 

 is indicated in the photograph, and all of the above eight re- 

 lated populations indicate a considerable interchange of gen- 

 etic elements. Number of specimens available, 50. 



Morph 10. Plate xxv. 



Point Caution is a rocky promontory on San Juan Island at 

 the northern entrance to Friday Harbor. The population fig- 

 ured inhabits a rather barren wind swept area where condi- 

 tions are unfavorable, and as a result the snails at maturity 

 produce shells of less than average size. In contrast with these 

 a population found upon the piling of the dock at the village 

 of Friday Harbor, in the interior of the bay, attain an unusu- 

 ally large size. Morph 18. Plate XXXIII. 



The shells of the snails in this morph, together with those 

 of neighboring populations, tend to exhibit a reduction in the 

 sculptural pattern, although in some cases a clinal system is 

 developed, ranging from strongly imbricated to perfectly 

 smooth shells. 

 Specimens available, 100. 



Morph II. Plate xxvi. 



Freeman's Island is a small reefy islet standing close to the 

 northwest border of Orcas Island, in the San Juan group. 



