REPORT ON XHE POLYPLACOPHORA. 



D. — ACANTHOIDEA. 



Insertion plates thrown forward. 

 * Plates broad, pectinated (Acanthoidea lophjroidea). 

 Sclerochiton, Carp. 



**Plates sharp, grooved outside (Acanthoidea typica). 



Acanthopleura, Guilding. 



a. Lucilina, Dall, 



b. Corephium, Gray. 



c. Francisia, Carp. 



***Plates sharp, smooth (Acanthoidea ischnoidea). 



Dinoplax, Carp. Nuttallina, Carp. 



Middendorffla, Carp. Arthuria, Carp. 



a. Beanella, Dall. Phacellopleura, Guilding. 



Section II.— CHITONES IEKEGULARES. 

 Tail plate abnormal, or with a sinus behind. 



E.— SCHIZOIDEA. 



Tail valve fissured. 



Lorica, H. and A. Adams. Schizochiton, Gray, 



a. Aulacochiton (Shuttleworth), Carp. 



F. — Placiphoroidea. 



Tail valve unslit, internally ridged, mucro nearly terminal. 



Enoplochiton, Gray. Placiphora, Gray. 



Ornithochiton, Gray. a. Fremblya, H. Adams. 



b. Euplaciphora, Shuttleworth. 



c. Guildingia, Carp. 



G. — MOPALOIDEA. 



Tail valve with posterior sinus and one slit on each side. 



Mopalia, Gray. Acanthochiton (Leach), Herrm. 



a. Placiphorella, Carp. a. Macandrellus, Carp. 



Katherina, Gray. b. Stedojrtax, Carp. 



Notoplax, H. Adams. 



