50 THE CONSTITUTION OF THE GASTROPOD PROTOCONCH, 



this score beg the indulgence of my readers, if it be found 

 that my nomenclature is out of date, and in view of the rapid 

 and manifold changes which historical research has of recent 

 years imparted to the face of Conchological literature, I fear 

 that this may be the case. 



The Constitution ov the Protoconch. 



The terms "Protoconch" and "Apex" are used here, as in 

 my last communication (30, 32), to designate those few early 

 whorls of the shell which differ in some marked character or 

 characters from the succeeding structure. It was in those 

 papers maintained that, as thus defined, the Protoconch may 

 have been formed "during one or more of four ontogenetic 

 stages." In accordance with this view I recognised four com 

 ponents in an ideally perfect Protoconch, and for these I 

 offered the following names and definitions (30, p. 327): — 



"1. Plyloeonrh. — This is the "primitive" shell of Lankes- 

 ter (35). It is formed by almost every member of the phy- 

 lum, but, with rare exceptions, it is shed at an early stage, 

 and does not enter into the composition of the protoconch. 



2. Veloconch — The greater portion of this is formed dur- 

 ing the Veliyer stage, though it may have been begun just 

 before that stage. 



3. Nepiocoiic/i. — This is formed during the Nepiomc stage, 

 but, for reasons given in a previous paper (29), I am inclined 

 to regard it as of rare occurrence. 



4. Ananeanoconeh . — Formed during early Neanic stages." 

 The formation of the Phyloconch cannot be assigned to any 



definite stage in the life-history. In Limncea xtagnalis the 

 primitive shell-gland is still in the form of a pit in the early 

 Veliger stage (Lankester) ; in Pntella the shell-gland has 

 opened out, and a shallow thimble-shaped shell is present 

 in the TroehoKpheic (Patten) ; whilst in many Lamelli- 

 branchs, the pit-like shell-gland appears in the Gastrula, 

 e.g. Ostren virgiriidDa (Brooks). In the first case it is 

 Typemhryonic, in the last Mefernbryonir^ using those terms 



