286 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



relations of its various genera, no dogmatism is justifiable at present or 

 until the characters of a much larger number of species have been de- 

 finitely determined. Until then, when the questions can be decided, 

 the various subdivisions will at least serve a very useful purpose in 

 calling attention to differences which otherwise might pass unnoticed or 

 unheeded. For my own part, my impressions are that the ma,iority of 

 the genera or subgenera proposed by Dr. Carpenter will eventually be 

 recognized as well founded, though a certain number may be condemned 

 to consolidation. 



NOTES ON THE GENERA. 



6. Cymatodus Carpenter, MS., not of Newberry, 1870, 



7a. Differs from LeptocMton not only in its hairy girdle, but also in 

 its valves, which are thrown forward, forming a decided transition 

 toward some of the palreozoic forms. Type LeptocMton curvatus Cpr. 

 Okosiri, Japan ; A. Adams. 



10. Microplax Adams and Angas 1864, not of Lilljeborg, 1865. 



12. Cailochiton (restricted). Laminae broken up into very numerous 

 teeth rising out of spongy eaves, and having a tendency to become 

 propped outside; sinus a mere wave in the united bodies of the sutural 

 laminae; mantle reticulated with peculiar bodies, the tips of which ap- 

 pear like diamond-shaped scales, and which are unlike the girdle- 

 armature of any other Chiton. Example Chiton Icevis of Montague, 

 Pennant and Gray. 



12a. Subgenus Stereochiton ; Cailochiton: zona coriacea sparsim 

 lanuginosa. Type Chiton castaneus Wood, Ind. Test, et Gen. Con.-h. 



15. Valvae tenues in zona tenui, levi, partim immersae; laminae inser- 

 tionis acutae, terminales pauci-flssatae, sed regulares; sinus baud den- 

 tatus; mucro medianus. Example, Chiton codrotatus Sowerby, Isle of 

 Bohol. 



17. Valvae parlim immersae; laminae acutae, Ischnoidae; sinus magnus 

 levis ; mucro medius planatus; zona spongiosa, antice producta. Ex- 

 ample, Spongiochiton productus Cpr., New Zealand, Mus. Cuming, no. 50. 

 This may be considered a partially covered Chcetoplenra , just as LeptopJax 

 is a partially covered Tonicella. 



20. Testa extus et intus ut in Callistochitone, zona porifera aliter 

 uuda. Type Chiton retusus Sby. China Seas. 



21. Testa extus et intus Ciiaetopleuroidea sed subgrundis parvis; zona 

 minutae squamulopilosa, fasciculis ad suturas instructa. {=IIanleyia Ad. 

 & Angas, non Gray). Type A. tetrica Cpr. -Ceylon. Mus. Cuming, no. 83. 



Hanleia variabilis Ad. and Angas probably belongs to this group, 

 but has not been dissected. 



23. Ceratophorus Carpenter MS. (non Diesing, 1850). Valvae extus et 

 intus Chaetopleurae similis, sed dentibus sufiultis, subgrundis curtis: 

 zona levis, in cornua sen cornuum fasciculas circa suturas et marginem 

 porrecta. Type Chiton Guildingi Keeve. 



