ARRANGEMENT OK FAMILIES OF MOLLUSKH. 26ii 



certaint}" from either the shell, operculum, external features, or 

 anatomj' of the animal ? 



"Whilst I shall continue to find in the shell the usual characters 

 for the discrimination of genera and families, I shall not refuse 

 all the aid which I can obtain from the study of lingaial dentition 

 as well as from all other sources which may enable me to more 

 rightly appreciate natural relationships, to correct error, to avoid 

 it. For the present, I prefer to treat Triton and Ranella as 

 transitional genera having many relationships with the Murices, 

 but partaking in their dentition and in some other structural 

 details in the characters of Cassis, Dolium, etc. 



Prof. Theodore Gill published in 1871, under the auspices of 

 the Smithsonian Institution an " Arrangement of the families 

 of Mollusks," largely founded on their lingual dentition. Whilst 

 this classification presents mariy features as novel as praise- 

 worth}^, reflecting the highest credit on the philosophical views 

 and critical acumen of its author, it is., I think, equally unac- 

 ceptable with those classifications heretofore proposed by 

 European authors in which this character has been used as an 

 exclusive guide. I reproduce Prof. Grill's arrangement : — 



Arrangement of Families of Mollusks. 



BY PROF. THEODORE GILL. 



(The figures in brackets refer to the illustrations of lingual 

 dentition in this xoork.) 



Class. A. CEPHALOPODA. 



Order 1. Dibranchiata. 



Suborder Octopodia. 



(0. littorales.) 



1. Cirrhoteuthidse. 2. Octopodidae (x, 1). 



( 0. pelagici ) 

 3. Philonexidae. 4. Argonautidse. 



Suborder Sepiophora. 

 (Oigopsidae.) 



5. Cranehiidse (including Loligopsidae). 6. Chiroteuthidse. 

 7. Onychoteuthidse. 8. Ommastrephidee. 



(Myopsidee.) 



9. Loliginidse (x, 2). 10. Sepiolidse. 11. Sepiidae. 

 12. Belosepiidse. 13. Spirulidfe. 14. Belopteridae. 



15. Belemnitidse. 



