*j6 CALIFORNIA ACADEMY OF SCIENCES. 



It has been supposed by some that S. raymondi is only 

 the young form of some rhomboidal species, but the fry 

 taken from shells like figs, i, 3, 4 prove their maturity,, 

 and we also give figures to show forms of the young. 



To settle the relation between it and the only other al- 

 lied species known on the West coast, as well as with 

 some Eastern forms, we figure several more for compari- 

 son. 



S. LENTicuLA Gould, figs. II, i8, 19. This figure (ii) 

 is taken from a specimen I obtained near Visalia, and 

 now in the State Museum, Berkeley. It differs from the 

 shell figured by Prime in a much more rounded form,, 

 greater convexity and a little larger size, showing that the 

 rhomboid outline and consequent truncation are not the 

 constant effects of full growth. It is shown by the fol- 

 lowing comparison that considerable vaj"iation exists in 

 the dimensions and proportions of adult examples from 

 various localities, the most northern being broader and 

 flatter, a difference apparently existing also in some 

 Eastern species. 



Figure. Length. Height. Diameter. 



Gould's type 18 0.43 0.37 0.18 (Prime.) 



Visalia examples n, 19 0.44 0.38 0.24 



Marin County examples 0.46 0.38 0.20 



The height and diameter are shown in diagram by figs. 

 18 and 19, by which it seems that the shell is sometimes 

 very near in convexity to S . ^partwneium Sa}^ and in one 

 of Prime's latest writings, quoted by Dr. Yarrow in the 

 quarto report of Capt. Wheeler's Aj-izona Expedition,, 

 1874, ^^ mentions specimens of S . lenticnla from there, 

 which were also intermediate between the type from Car- 

 son River and partiiinciiini, suggesting that this form 

 (fig. 11) is merely an extremely inflated form of lenticnla. 



The description of ".5. fartnnicittm'' by Prime alsO' 

 includes three forms varying in size, in convexity, and in 



