POLYPLACOniH:\. 



ee. Anterior \ 



larly spaced, mon- than "> ; j.o.st-i 

 valve with :i median angular t 

 its edge with several uni-<|ual notched 

 or slits; exposed part of valves flask- 

 shaped I\ \iiii 

 eee. Anterior valve having 6-8 un< 

 slits; posterior valve 2 slit- ai, 

 median wave; expoM.I part of each 

 valve far shorter than the ridge of the 

 valve, heart-shaped A.MICULA. 

 dd. Valves completely covered by the girdle, 



their apices not marginal, CRYIT<M m 

 b. Median valves partly lacking side slit- ; tail valve with 

 2 or no slits 



cc. Posterior valves without distinct slits, and huvini: 

 no posterior sinus ; more or less hollowed out and 

 funnel-shaped ; anterior valve with 3-5 slits ; body 

 rather vermiform ; gills short, posterior (Cryptopla- 

 cidce ; see next volume for species). 



d. Valves small, narrow and sagittate, gener- 

 ally partly disjointed ; not covering the 

 body to any considerable extent 



CRYPTOPLAX. 



dd. Valves transverse/all strongly imbricating ; 

 covering a considerable portion of the upper 

 'surface CHONEPIAX. 



aaa. All valves, or valves i-vii, possessing insertion plates cut 



teeth by slits ; the teeth sharply sculptured or "pectinated " out- 

 side by fine vertical grooves (Chitonidce). 

 b. Valves lacking eyes (Chitoninoe). 



c. Girdle scaly CHITON, p. 141. 



cc. Girdle leathery, with short bristles 



EUDOXOCHITON, p. 192. 



bb. Valves having eyes ; posterior valve not deeply simiM-d 

 behind, its insertion plate developed (Tonic! ; 



c. Girdle leathery, nude or nearly so,ToNiciA. j>. L94, 

 cc. Girdle covered with calcareous spines or spinelets, 



ACANTHOPLEURA, p. 213. 



bbb. Valves having eyes (rarely subobsolete) ; posterior 



