450 NOTES ON PKOSOBKANCJIIATA, 



(leinonstrated in other Mollusca;* we are therefore led to the 

 following definition of the nepionic stage in the Gasteropod 

 mollusc : — lliat sUiye diiring ?chich the velum undercioes degenera- 

 tion and disappears. 



And a theory I advanced some time ago is still maintained, 

 namely: — Where no variv is fJwowji up at the condasion of the 

 embryonic shelly no conchglaceons record of the nepionic stage has 

 been left by the mollusc. 



A more explicit definition of the nepionic stage than Buckman 

 and Bather's would be -.—That stage during which the larval 

 organs become aborted. The above delinition of this stage in the 

 Gasteropod ^Mollusc is, tlierefore, only a specific form of the 

 general definition. 



It has been suggested to me in the course of discussion that 

 the pseudoprotoconch is the homologue of the above varix. This 

 suggestion is a good one, and it is likely that some pseudoproto- 

 conchs are nepionic, but it does not apply to those of Lotorium, 

 as shown by the extreme thinness of the calcareous lining of the 

 young specimen described above. 



C. A SHORT LIST OF WORKS IN WHICH PrOTOCONCHS ARE DESCRIBED, 

 OR IN WHICH THE AUXOLOGICAL TERMS ARE DISCUSSED. 



1. — Baker, F. C. — "On the Modifications of the Apex in Murex." Proc. 



Acad. Nat. Sci. Philadelphia, 1890, p. 66 et seq. 

 2. " Descriptions of New Species of Muricc'.<, with remarks 



on the Apices of certain forms." Proc. llochester Acad. Sci. i , 1891, 



p. 129 ct .^eq. 

 8. " Modification of the Apex in Gasteropod Molkisks." 



Ann. New York Acad. Sci. ix., 1897, p. 685 tt seq. 

 4.— Dall, W. H.— '"'Blake Mollusca." Pt. ii. Bull. Mus. Comp. Zcol. 



Plarvard Coll. xviii., 1898. 

 5. " Tertiary Mollusca of Florida." Trans. Wagner Free 



Inst. Sci. iii., pts. 1 and 2, 1S90 and 1892. 



* Fide Korschelt & Heider, Text Book of Emb. Invert. M. F. Woodward's 

 edit., iv., p. i;?3. 



