— 12 — 



ii. Valves niai-ked with concentric ridges and sometinics ribs. 



j. No ladiating ribs, concentric ridges low, rounded, occasionally 



dividing into two, covered with a heavy, glossy, persistent 



periostracvnn ; pallial sinus reaching about half way to 



anterior miiscle sear ; valve margin smooth ; shell white. 



Sea cockle Ainiantes callosa 



p. 34 ; pi. 5 , fig. 3 



jj. Radiating ribs picsent, concentric ridges not smoothly rounded 

 n(jr dividing, with thin, grey, easily detached periostracum; 

 pallial sinus small, not deeper than diameter of posterior 

 muscle scar; valve margin roughened; shell greyish. 

 Hard-shell cockles Chione 



k. No distinct lunule or escutcheon, ribs more prominent than 

 concentric ridges in posterior 5 of valve ; pallial sinus 

 acute. 



C. fluctifraoa 



p. 37 ; pi. 9 , fig. ] 



kk. Distinct lunule and escutcheon present, concentric ridges 

 usually more prominent tlian ribs in all parts of valve ; 

 pallial sinus rounded. 

 1. Numerous thin, concentric ridges, ribs eveiywhere small 

 and inconspicuous. 



C undatclla 



p. 37; pi. 9, fig. 2 



1 



Fig. 11. Chione succhictd. One and one-third times natural size. 

 (A) Exterior anterior end. (B) Interior right valve. 



11. Concentric ridges heavier and less numerous, ribs at pos- 

 terior end more distinct than elsewhere but not more 

 conspicuous than ridges. 



C. succincta 



p. 37 ; pi. 9 , figs. 3, 4 



lih. Ligament internal, valves lighter, tliin and sharp at edges. Size 

 modei-ato or large, pallial sinus reaching 5 to i distance to 

 anterior muscle scar. 



Dish shell Spisiila 



p. 54 



dd. .\ninial asymmetrical with valves unlike especially at sipbonate end; shell 

 usually thin and weak particularly at margins (least marked in Semele 

 and TeUiva) ; siphons separate, slender and very long: forms deeply bur- 

 rowing in sand or mud where they are found lying on the side, 

 e. Ligament wholly external ; pallial sinus united with pallial line ; shells 

 generally thin, 

 f. Shell elongated (about twice as long as wide), periostracum not con- 

 spicuous, shell not conspicuously thin, whitish with fine but very 

 distinct and regular growth lines, siphonate end bent to the right. 

 Tellen TrUina bodegensis 



p. 42 ; pi. 11 , fig. 1 



