“1892. PROCEEDINGS OF THE NATIONAL MUSEUM. 189 
Genus SAXIDOMUS Conrad. 
Saxidomus aratus Gld. (S. gracilis Gld.). 
Often washed ashore in the spring. This shell, like others of the 
family, varies in form. 
Saxidomus Nuttallii Conr.? 
Beach-worn valves; may be specimens of the preceding species. 
Genus RUPELLARIA F. de Bellevue. 
Rupellaria lamellifera Conr. 
Two dead shells reported. 
Family PETRICOLID 2. 
Genus PETRICOLA Lamarck. 
Petricola carditoides Conr. 
Only dead ones collected. 
Petricola cognata Ads. 
One broken valve. (W. H.D.) Mrs. Trowbridge. 
Petricola tenuis Ads. ? 
One, young, dead. (C.T.8.) Ifnota form of carditoides this has 
hitherto been known only from the southern fauna. 
Family CHAMID_®. 
Genus CHAMA Brug. 
Chama exogyra Conr. 
Common on rocks, from which they are hard to remove, even with a 
hatchet, as one valve usually adheres firmly. Both sinistral and dex- 
tral shells occur in the same colony. 
Chama pellucida Sby. 
This species is more pellucid and frilled, and often of a bright rosy 
tint in some places. It is usually washed ashore from deep water. 
Chama spinosa Sby. 
Very rarely washed ashore. These three forms are sometimes diffi- 
cult to distinguish; one species appears to run into another. 
Family CARDITD.. 
Genus CARDIUM. 
Cardium centifilosum Cpr. 
One valve; Mrs. Trowbridge. Abundant in 16 fathoms at Catalina 
Harbor. (W. H. D.) 
