PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 297 



Ischnoradsia Cpr. non Slmttleworth. 



I. trifida Cpr. Minor lateral with no outer wing, but a small process near the 

 apex of the shaft, which may represent it; inner wing normal; major lateral shaft 

 normal, cusp bidentate, with a spot behind the notch (Fig. 17 a); uncini rugose, 

 normal. Fig. 17. 



Lepidopleurus Cpr. non Risso. 



L. Mertensii Midd. Minor lateral with no outer wing; shaft cusped at apex, inner 

 wing normal; major lateral with a simple cusp, shaft normal, deeply channelled 

 behind. Fig. 18. Fig. 18 a shows the appearance of the minor laterals and their 

 wings extending behind the rhachidian tooth as they do when in their natural posi- 

 tion. 



Lepidoradsia Cpr. (Lophyrm pars Adams.) 



L. australis Sby. Minor lateral with a singular mushroom-like cusp with rudi- 

 ment of inner and no outer wing; major lateral bidentate, shaft keeled with spatu- 

 late process; major uncinus short, broad, other uncini rather small. Fig. 19. 



Callistochiton Cpr. 



C. palmulatus Cpr. Minor lateral with a narrow inner wing parallel with and no 

 wider than the shaft, cusped at the top, outer wing absent or represented by a 

 minute cuspidate process; major lateral with a simple cusp, shaft with an anterior 

 keel bearing a sublanceolate process. Fig. 20. 



Callistoplax, Ceratophorus, and Xewcombia not examined. 



Pallochiton Dall (= Hemphill ia Cpr. MSS. nom. prseoc). 



P. lanuginosus Cpr. Minor lateral normal, bi-alate; major lateral tridentate, shaft 

 normal. Fig. 21. 



Lophyroidf.a. 



Chiton Cpr. Lin. not Adams. Type C. tuberculatum Lin. (Lophyrus H. & A. Ad. not Poli). 



C. articulatus Shy. Minor lateral with no outer wing, shaft small, narrow, prone, 

 from which extends the greatly elongated cusped inner wing external to the rha- 

 chidian tooth ; major lateral with a simple rounded yellowish cusp with a black 

 margin marked by a peculiar spot ; shaft normal, with an inner lateral expansion pro- 

 duced into a lingniform process; major uncinus broad, long, spatulate; outer unci- 

 nus transversely elongated. Fig. 22. Fig. 22 a, side view of rhachidian tooth. 



C. Stokesii Brod. Minor lateral with expanded inner wing, shaft cuspidate, cusp 

 twisted and outer wing reduced to a portion of this cusp or absent ; major lateral 

 with an elongated simple cusp, shaft thick, strong, keeled in front, keel bearing a 

 blade-shaped process attached to the keel at two points, with a small foramen between 

 them; major uncinus short, broad, somewhat plume>shaped. Fig. 24. Fig. 24a, 

 major uncinus, from below. 



C. Cumingii Frembly. Minor lateral normal, with wings recurved above and on 

 each side; major lateral with simple elongate cusp, shaft with a strong keel bent 

 outward below and produced above into a strong spoon-shaped process; two inner 

 uncini nodulose : major uncinus with a slender and rather straight shaft. Fig. 25. 



C. assimilis Rve. Minor lateral; shaft with small or nearly abortive wings, ba-se 

 long and recurved; major lateral with a simple rounded cusp, a keel on the shaft 

 bearing a spatulate process; major uncinus feather-shaped, the vane on the inner 

 side. Fig. 26. 



Tonicia Gray. 



T. elegans Frembly. (Type.) Minor lateral leaf-shaped, normal, apex curved for- 

 ward; major lateral with an orange, black-edged, rounded, simple cusp with a spot 

 on the margin, shaft normal; major uncinus very much twisted and deenrved, 

 spatulate. Fig. 27. 



Radtsia, Fanny id, Eudoxochiton, and Craspvdochiton not examined. 



