24 CHITOXID^E. 



Subfamily ISCHNOCHITONIN^E. 



Ischnoidea CPR., Table of Regular Chitons, and DALL, Proc. U. 

 S.Nat. Mus. 1882, p. 283, (in part; Genera 19-24 excluded). 

 IschnochitonidcB DALL, ' Blake ' Gastrop. p. 415, 1889. 



I have above given some of the reasons which induce me to con- 

 sider this group as a subfamily rather than a family. I am wholly 

 disposed to believe that the subfamily as here constituted, is rather 

 artificial ; and some of the genera may require consolidation. The 

 relation existing between Chcetopleura and Tonicia especially calls 

 for investigation ; and there are some forms (section Cyanoplax) which 

 seem to bridge the gap between Chcetopleura and Tonicella. 



Synopsis of Genera of Ischnochitonince. 

 Genus V. LEPTOPLAX Cpr. 



Valves thin, partly immersed in the thin smooth girdle ; insertion 

 plates acute, having few slits. Umbo of posterior valve median. 



Genus VI. SPONGIOCHITON Cpr. 



Valves partly immersed. Insertion plates acute; umbo of pos- 

 terior valve median. Girdle spongy, having chaffy scales and hair- 

 lets, and produced forward. 



Genus VII. CH^TOPLEURA Shuttlw. 



Valves exposed ; insertion plates smooth or obsoletely grooved 

 outside; eaves solid; umbo of posterior valve central or anterior. 

 Girdle leathery, more or less hairy. 



Genus VIII. TONICELLA Cpr. 



Valves exposed ; insertion plates smooth or slightly grooved out- 

 side ; eaves spongy ; umbo of posterior valve anterior. Girdle 

 leathery and smooth, without scales or hairs. 



Genus IX. SCHIZOPLAX Dall. 



Valves exposed, and similar to those of Tonicella except that the 

 intermediate valves have & median' longitudinal slit filled with cartil- 

 age. Eaves very spongy. Girdle leathery, as in Tonicella. 



