N0.1149. NOTES ON CYTHEREA CRASSATEIJAHhES—tSTEAKNS. 2>11 



INTERIOR COLORATION. 



Occasionally individuals are found in which the muscular scars arc 

 pale to dark chocolate, with a touch or tint of bluish purple. In a sin- 

 4>le example the whole of the inside of both valves was stained with 

 bluish chocolate, the rej^ion of the muscular scars being darker than 

 elsewhere. Oidinarily the inside of the valves is of a uniform white- 

 ness, rarely showing a. yellowish tinge. 



VARIATION IN FORM. 



From color variation we tome to variation in Ibrm. As a whole, with 

 a thousand or more examples under review, the form is found to be 

 remarkably constant. The outline of a few extremes is herewith given. 



The smallest, a junior (IMate XXIV, tig. 1), is unusually triangular 

 and short; the only example in the large number I have com])ared. 

 The next in size (Plate XXIV, fig. 4) is unusually elongated trans- 

 versely, one of three. 



The larger outline (Plate XXIV, fig. U) is that of a specimen from the 

 outer beach of Coronado Peninsula, San Diego, contained in the collec- 

 tion of Mr. Uomer Hamlin, of Los Angeles. Here we find the anterior 

 portion greatly produced, as will be seen by comparison with the mid- 

 dle outline (Plate XXIV, fig. .J), which is a fair representation of the 

 ordinary run of specimens, which are nearly if not quite etiuilateral. 



The large San Diego specimen is from a special habitat, indicating 

 the deeper burrowing or holding on necessary in a rapid tideway, or on 

 a shore where the water deepens (quickly and is more or less turbulent. 

 With the greater depth of imniersion in the sea bed follows the neces- 

 sity for greater length of si])hons and increased length of shell by the 

 building up or development of the valves in that portion for the pro- 

 tection of the soft parts, and we have here an illustration of the rela- 

 tion of the environment to form, as is also well shown in the large 

 Cardium [C. mQ/jnuni) of Florida, when examples from portions of the 

 wave- washed Atlantic shore are compared with those from the quieter 

 beaches on the Gulf side. 



