480 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.38. 



direction as the Qudibranchs among opisthobranchs, and the slugs 

 among pulmonates, the direction, namely, of loss of shell. This loss 

 apparently proceeds by a kind of combination of the methods seen in 

 nudibranchs and slugs, for there is an embryonic "nautiloid" shell 

 afterward shed as in nudibranchs, while the post-embryonic shell is 

 overgrown by a notseum and degenerated as in slugs." It may not 

 be wholly a coincidence that the group has developed feeding habits 

 (on compound ascidians) recalling the uudibranchs and has become 

 (at leas! in part) like them, hermaphroditic The aberrant character 

 of the group appears in the well-known and extraordinary "nesting" 

 habit in a hole made in the ascidian colon\ and com red with an 

 "operculum." It further appears in the sudden radical departure of 

 one section of the group from the tsenioglossate type of dentition.'' 



It would seem that the host provisional treat incut of the family is 

 as follows: 



Family LAMELLARIIDiE (various family characters in nervous 

 system, stomach, etc. Consult Bergh). 



Subfamily L amki.lakiin .k (Radula 11 -1, of aberrant form. 

 Sexes separate. Shell few whorled, wholly internal, but calcareous 

 though sometimes very degenerate." No expiratory cleft. Nearly 

 world-wide but especially tropical). 



Genus Lamellaria Montagu (part ), 1815 (syn. includes Corinalla 

 Blainville, L824, Oryptothyra Menke, 1830, Marsenia Leach, 1847, 

 Cry ptocella II. and A. Adams, 1853, Ermea Gray, 1S57). 

 Subgenus Mars< nulla Ber<di. 

 Subgenus Chelynotus (Swainson, L849) Bergh. 



Subfamily Ykliti \ in.k. (Radula 2-1-1-1 2, of aaticoid form. 

 Sexes united. Shell progressively degenerating from several whorled, 

 external, calcareous though thin, to a mere internal horny scale. 

 Expiratory cleft developed where shell is internal. Boreal except 



( '(tit (loll 11 llil . I 



Max it In- t luu the spicules of the dorid nudibranchs represenl an exactlj similar 

 phenomenon? li has been generally assumed that the loss of the nautiloid embryonic 

 shell ends the shell-history of the individual dorid and thai the spicules with which 

 the notseum is so plentifully besel represenl a novel formation. The Bame assump- 

 tion might have been made for Onchidiopsis were not the shell, especially in the specieB 

 heiv described, still unmistakable as such. In other words, ii we use the historj of 

 tin- shell in Onchidiopsis, which is still decipherable, as a key to read the history of 

 the shell in the dorids, where it is no1 clearly decipherable, we shall conclude that 

 the Inst "nautiloid" shell is only the protoconch and shall homologize the spicules 

 of the adult notseum with the adult internal shell of Onchidiopsis. There is nothing 

 in the morphological relations of the notseum and mantle i" forbid this, and it seems 

 tn the writer worthy of serious consideration. 



b The strikingly parallel aberration of the subgenus Turritellopsis, in the Turritel- 



lidse, sh'iitld be compared, however, as an illustrati f how profoundly and suddenly 



the tsenioglossate typ£bf dentition may be modified w ithoul anyapparenl greal cha 

 in the rest "i" the organism. Figures may be found in Tryon's Manual. 



C'Presque membraneuse," L. leptolemma Bergh. 



