43 



present, leading to forms that arc heavily pigmented, suggests 

 a genetic system comparable to that found in polymorphic 

 terrestrial gastropods, such as Cepaea^ Achatinella and Cerion. 

 In the case of Cepaea according to Lamotte (195 1) coloration 

 is governed by several sets of alleles, the albinic condition 

 being recessive to color, and whole color dominant to banding. 

 In populations oi lamellosa we commonly find a graded series 

 ranging from pure white to heavily pigmented forms, suggest- 

 ing the interaction of several allelic components. Yellow color, 

 as is suggested by some of the observations made by Moore, 

 apparently is governed by a separate genetic element. 



The sculpture in this species appears to be governed by 

 three independently acting genetic elements, involving the 

 spiral bands, the vertical lamellation and the secondary spirals. 

 The latter, which arc a conspicuous feature in some of the 

 related forms, are seldom seen in populations oi lamellosay and 

 when present are feebly expressed, as may be noted in some of 

 the specimens illustrated on Plates xvi-xix. 



The primary spirals are subject to a wide range of variation, 

 which seems to be expressed independently of the vertical 

 lamellae. In some cases it is sharply defined, and dominates 

 the sculptural pattern, as may be seen in the population de- 

 rived from Trinidad, California, illustrated on Plate xix. We 

 have here an indication of the relationship o( la?nellosa to the 

 common muricid stem. In other cases the spirals may be so 

 reduced as to be practically obsolete, or only feebly indicated 

 on the terminal portion of the last whorl, as may be seen in 

 populations such as are illustrated in Plates ix-xviii. On the 

 other hand the spirals may be distinct but are combined with 

 incipient lamellae, as is illustrated by the figures in Plate xxii. 

 In still other cases both spirals and lamellae are sharply defin- 

 ed so as to give the shells a cross-hatched appearance, as seen 

 in Plate xl. In some extreme cases the vertical lamellae are 

 more or less elevated, and the spirals are faintly indicated as 

 modifying the contour of the lamellae: an example will be seen 

 illustrated in Plate L. 



