344 CHITONID^. 



BEANELLA, Dall. (Beaiiia, Cpr., not Johnstone.) Armor and 

 girdle intermediate between Acanthopleura and Ischnochiton ; 

 mucro submedian ; the laminse acute ; the girdle scaly, subspinose, 

 scarcely imbricated. C. Bissoi, Cuming. 



ARTHURiA, Carp. Armor thin ; valves waved ; mucro posterior, 

 produced ; laminse acute, smooth ; last valve extending forwards, 

 sinus planate, laminate, smooth ; girdle coriaceous, smooth or 

 downy. G. filosus, Cpr. 



NUTTALLTNA, Cpr. (Named in honor of Prof. Thomas Nuttall, 

 a pioneer collector of Californian shells.) Shell elongated, valves 

 projecting anteriorly ; mucro posterior, elevated ; laminse acute, 

 smooth, elongate ; central valves bifissate ; sinus riot laminated, 

 planate ; girdle spinose. Differs from Acanthopleura in the 

 smoothness of the sharp teeth, in their great length and Radsioid 

 slitting; in the thrown-back mucro, which often projects bej^ond 

 the margin ; in the throwing forward of the rest of the shell, as 

 in Katherina, and in the deep spongy flat sinus which interrupts 

 the sutural laminse. G. scabra, Reeve (Ixxxvi, 85). 



PfiACELLOPLEURA, Guild. Posterior valve thrown forward, 

 having six or more slits; anterior valve with five slits; middle, one 

 slit ; teeth very long, sharp, smooth ; eaves very short ; sinus 

 narrow, laminse separated ; girdle thin, downy, wide, with sutural 

 pores. G . porphyriticus, Reeve. 



Section II. — Chi^ones irisgulares. 

 Tail-plate abnormal or with a sinus behind. 



E. Schizoidea. 



Tail-valve fissured. 



LORiCA, H. and A. Adams. Insertion-plates regular, posterior 

 valve slit between two ridges ; anterior valve with many slits, 

 middle with one ; teeth blunt, rugose ; eaves moderate ; sinus 

 narrow, girdle slit behind, smooth, scaly. G.cimolius (lxxxvi,86). 



AULOCHiTON (Shuttl.), Cpr. Mucro posterior, slightly sinuate; 

 sinus lobed ; girdle covered with small scales, produced in front. 

 G. Angasi, H. Ad. 



scHizocHiTON, Gra3^ Insertion-plates straight forward, deep 

 slit, slits many in anterior valve, one to two in middle, few in 

 posterior valve ; teeth sharp, long; eaves small; sinus narrow, 

 very deep; girdle slit behind, covered with minute spiculse. G. 

 incisus. 



P. Placiphoroidea. 



Tail-valve unslit, internally ridged, mucro nearly terminal. 



ENOPLOCHiTON, Gray. Insertion-plates straight forward, flat 

 behind ; anterior valve with many slits, middle with one, posterior 

 with none ; teeth serrate ; eaves moderate ; sinus deep, lobed ; 

 girdle large, with separate scales, and bristles between, G. 

 Goquimbensis, Fremb. (Ixxxvi, 87). 



