328 NOTES ON PROSOBRANCHIATA, IV., 



which led to its discovery in the above instances will its presence 

 or absence be demonstrated in any protoconch. 



The veloconch is of very general occurrence throughout the 

 Gastropoda, occurring even in many of the molluscs which in 

 later life are without any trace of shell {jEoUs, etc.). It may be 

 succeeded by either nepioconch (Murex denndata Perry) or 

 ananeanoconch (Oymatium), may be distinctly marked off from 

 the succeeding portion (Murex, Bolmm, Cassis, Cajyulus, etc.)^ 

 or may be undefinable as to its ultimate limit {Triphora, some 

 Cymaiia and Systra), may be retained throughout life, or lost by 

 abrasion and corrosion {^Triphora, Meg a I atr actus) or shed, by 

 testaceous as well as naked molluscs, at an early age {Cymatium). 

 Finally, it may be either of the same substance as the adult 

 cuticle or periostracum [Cymatium) or it may be calcareous 

 {Murex, Triphora). 



The nepioconch is perhaps existent only as the varix which 

 divides the protoconch from the succeeding adult structure, as 

 typified in some Murices and Fusi; it may also be represented by 

 some of the smooth protoconchs which have been moulded inside 

 a horny veloconch, which was later shed. In a previous paper, 

 however, wherein I have discussed the nepionic stage at some 

 length, I showed that such casts are sometimes ananeanic 

 structures (4 vide also 3), 



The ananeanoconch, whilst present in all shells, unless lost by 

 abrasion or corrosion, may be a component part of the protoconch, 

 but may, as in Murex and some other genera, be a portion of the 

 true conch. The name, it must be remembered, designates, not 

 some particular portion of a shell, but any portion formed during 

 a particular stage of development; thus maj^ it be either pro- 

 toconch or true conch. The ananeanoconch of Cymatium is 

 formed after the pelagic larva has come to rest, and has lost the 

 velum; it is in this instance moulded inside the horny veloconch, 

 which is later shed; there is no nepioconch. In Jfelo and Mega- 

 latractus it was formed in the egg-capsule and was deposited 

 inside a horny covering, but this latter is perhaps more nearly 

 analogous to the adult periostracum than to the veloconch of 



