28 University of Michigan 



laterals, the ventral being especially high and lamellate ; right 

 valve with two, parallel, oblique, usually lamellate pseudo- 

 cardinals, although the upper is vestigial or sometimes almost 

 completely lacking, while the lower in old shells tends to become 

 almost trigonal ; and with one thin lateral ; beak cavities mod- 

 erately deep, capacious, obscuring the dorsal pits anteriad ; 

 anterior muscle scars well marked, smoothish, separated ; pos- 

 terior scars larger, confluent, not impressed, concentrically 

 striate and iridescent ; pallial line well marked throughout its 

 length ; nacre white, or tinted with lavender or salmon, some- 

 what thickened anteriad and delicately iridescent throughout. 



The male( ?) shell (plate VIII, figs. 39 and 40, type) is sub- 

 rhomboid, with the posterior ridge better marked and ending 

 in a rounded point about one-half way up on the posterior 

 margin. The female (?) shell is more elongate, subovate, and 

 strongly inflated in the posterior half of the shell, with the 

 very much rounded posterior point one-half or more of the 

 height above the ventral margin (plate VIII, figs. 41 and 42). 



This subspecies is apparently a smaller form of the more 

 southern typical rovirosai. The adult female(?) shell also 

 differs from the type specimen, by a tendency to be somewhat 

 more strongly inflated and elongate. 



Simpson (1900) first pointed out that U. testndincus Reeve 

 differed from true cxplicatus Mdrelet, and named the form 

 L. lividus. Although I must confess that I am unable to place 

 some individuals to my complete satisfaction, I think that the 

 two shells, as Simpson intimated, are not even very closely 

 related. But, from the material on which the subspecies is 

 based, U . testiidineiis or L. lividus appears to represent a rather 

 unpronounced female type, while rovirosai (type in A. N. S. 

 P.) is what I believe to be the completely developed, old female, 

 which has a type of marsupial ( ?) swelling quite distinct from 



