68 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



3. Adult shell 55 mm or higher; left valve with 9-10 pri- 

 mary and 10-11 secondary ribs, right valve with 9-10 

 pairs; interior predominantly white 



4. Primary ribs of left valve with very long spines, 

 secondary ribs very low and with very short spines ; ribs 

 of right valve with long spines on central riblet and 

 much shorter ones on adjoining riblets .... 



hastata (Sowerby) 



(Monterey to San Diego, California) 

 4. Primary ribs of left valve with moderately long spines, 

 secondary ribs about half as high as primaries; ribs of 

 right valve with moderately long spines on central rib- 

 let and shorter ones on adjoining riblets .... 



hastata hericia (Gould) 



(Gulf of Alaska to Santa Barbara, California) 

 3. Adult shell less than 35 mm high ; ribs of each valve nearly 

 equal in size and spines quite short; fine punctate sculp- 

 ture covering disks ; posterior auricles obliquely truncated ; 



interior nearly always red or red-orange 



hastata pugetensis (Oldroyd) 



(Prince William Sound, Alaska, to Newport Bay, Cali- 

 fornia) 

 2. Ribs narrow, rounded plications of disks ; adult shell less than 

 24 mm high; ribs with central row of fine spines flanked by 

 two low spinose riblets near ventral margin ; interspaces with 

 a low spinose riblet ; internal surfaces of interspaces angulate- 



ly ridged loiuei (Hertlein) 



(Galapagos Islands; Ecuador to northen Gulf of California; 

 western Lower California north to San Benito Islands ; Santa 

 Catalina Island, California) 

 1. Shell thicker and without spinose sculpture 



5. Right valve with 21-30 low, flat and dichotomous ribs 



6. Left valve with interspaces concentrically ridged and with 

 low central riblet; left valve white, with ribs brown or 

 red ; posterior auricles obliquely truncated .... 

 patagonica (King) ; ?afnandi (Hertlein) 

 (Puerto IVIontt, southern Chile, to Strait of Magellan; 

 also in Atlantic, from Strait of Magellan north to Puerto 

 Quequen, Chubut Territory, Argentina) 

 6. Left valve without concentric ridges but with fine reticu- 

 late sculpture; low riblet usually present in interspaces; 



