Plaxiphora. ] 



AMPHINEURA. 



17 



Genus 2. PLAXIPHORA, Gray, 1847. 



Plaxiphora, Gray, P.Z.S., 1847, 65, 68, 169. Type : Chiton setiger, King. 

 Placiphora, Cpr. MS. and Ball, 1881. Placophora, Dal) ; not Placophorus, 

 Mulsant, 1873. Euplaxiphora, Shuttleworth. Chcetopleura (part), Roche- 

 brune, not Chcetopleura, Shuttleworth. (Pilsbry.) 



Valves mostly exposed, all having insertion plates developed, that 

 of the anterior valve normally with 8 (sometimes 7-9) slits. Median 

 valves 1 slit. Posterior valve having the insertion plate smooth, 

 unslit, interrupted behind by a median rounded sinus, which does 

 not generally emarginate the tegmentum ; mucro posterior. Girdle 

 bearing simple bristles or hairs, scattered or gathered into pores or 

 tufts at the sutures. 



Subgen. 1. PLAXIPHORA, s.s. 



Slits of anterior valve normally 8, corresponding in position to 

 external ribs ; the teeth long outside. Girdle widest at the sides. 

 Mantle not fringed in front of the head. 



Distribution. Southern extremities of the southern continents : 

 New Zealand, Australia, Tasmania, South Africa, Tristan da Cunha, 

 and South America. 



KEY TO SPECIES. 



A. Valves exposed. 



a. Posterior valve not greatly reduced in size or altered in 



form. 



b. Central areas unsculptured save for growth-lines, 

 c. Sutural pores or tufts distinctly developed. 



d. Lateral areas with 2 to 4 low, flat ribs ; shell 



large . . . . . . . . superba. 



dd. Lateral areas with 2 raised, rounded ribs ; 



shell small . . . . . . . . aucklandica. 



cc. Sutural pores absent, girdle densely covered with 



bristles . . . . . . . . . . glauca. 



bb. Central areas sculptured, at least at the sides, 

 c. Sculpture rather coarse. 



d. Shell large ; sutural pores with bifurcating 



bristles ; girdle broad, reddish . . biramosa. 



dd. Shell small ; sutural pores with more than 2 

 bristles ; girdle narrow, white or white 

 and black . . . . . . . . ccelata. 



cc. Sculpture excessively fine . . . . . . Murdochi. 



aa. Posterior valve reduced to a narrow crescentic form, 



strongly arched upwards . . . . . . . . ovata. 



B. Valves partially immersed in the girdle, which encroaches at the 



sutures ; no sutural pores . . . . . . . . obtecta. 



Sect. 1. PLAXIPHORA, s.s. 

 Euplaciphora, Shuttleworth, not Carpenter. 



Valves exposed. Entire shell normal in form ; posterior valve not 

 greatly reduced in size or altered in form. 



