132 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Genus ALIGENA H. C Lea, 1845. 
Shell rounded, triangular, inflated; single small anterior tooth under 
the beaks, separated by a gap from the surface of attachment, under the 
posterior dorsal margin, of an elongate internal resilium carrying a 
lithodesma. Pal. San Pedro. (Arnold.) 
Type. Aligena striata Lea. 
Range. California to Lower California. 
Range in time. Miocene, Pleistocene. 
Aligena cerritensis Arnold, 1903. 
Pal. San Pedro, p. 138; pi. 13, fig. 3. 
Shell small, rounded, triangular, inflated, thin; inequilateral, the umbo 
being nearly terminal posteriorly; anterior dorsal margin nearly straight; 
anterior extremity quite sharply rounded and produced furthest below 
middle; posterior extremity sloping off abruptly from umbo and rounded 
near the base; ventral margin arcuate with faint concentric sculpture; 
umbones small, pointed anteriorly twisted, with a minute tooth below them 
on the cardinal margin; pallial line entire; muscle scars subequal. Length, 
8.6; height, 8; diameter, 5 mm. (Arnold.) 
Type in U. S. N. M. Type locality, Upper San Pedro series, Los 
Cerritos. 
Range. La Jolla, California, to Magdalena Bay, Lower California. 
In the Pleistocene at San Pedro, California. 
Genus ROCHEFORTIA Velain, 1846. 
Shell ovate or rounded-triangular, periostracum adherent, usually 
polished; individuals free or domiciliary in the burrow of crustaceans. 
(Dali.) 
Type. Rochefortia australis Velain. 
Distribution. Northern Pacific and Atlantic oceans. 
Rochefortia tumida Carpenter, 1864. 
Plate 54, figs. 11 to 14. 
Suppl. Rep. Brit. Assoc., p. 129. Proc . U. S. N. M., 21; pi. 87, fig. 7. 
Shell subelliptical, both ends broadly rounded, lines of growth fine, 
ossicle minute. (Carpenter.) 
Type in U. S. N. M. Type locality, Vancouver Island, British Columbia. 
Range. Shumagin Islands, Alaska, to San Diego, California. 
Rochefortia planata Dali, 1885. 
Arch. f. Naturg, 51:34. Proc. U. S. N. M., 21; pi. 88, fig. 12, 1899. 
Testa minuta, forma oblique ovata, extremitate antica producta, postica 
brevissima margine ventrali convexo, posteriore abrupte declivi; valvulae, 
