P r. A T E XT.. 



IM.KirKM-; l'K(TEN8. 



[rnk'ss oilierwise stilted all figures are iipi>roxiiiiately natural size. The light in these two figures eomes frmn tlie 

 right-liaiKl side. Sprciineii not coateil i^y Williams proce.ss. I'hotograplis by Ralpli Arnold.] 



i-age. 



Kic;. 1. I'iftii, { .\,j(lijjci'lrji) nvi/c/i/i (ialili. \' . C. Typo lOti 



E.\terior of right valve; altitmlf l:iil luiu., X ji- I'lincenc, ('erri)si Island, off Lower 

 ("alifornia. (M. B. ) 



Fio. III. Same speciiiieii as lij;. 1 106 



E.xterior of left valve. (M. 1'.) 



224 



