BY H. LEIGHTOX KESTEVEN. 459 



the fact that the apices of adult specimens from which the external 

 coating had been removed, were entirely demolished by the same 

 treatment. In none of the species studied has it been found 

 possible to define a nepionic stage; in every instance the sculpture 

 of the postembrj^onic structure, which immediately adjoins the 

 protoconch, is, in miniature, that of the adult; nor is there in any 

 of the species a varix formed of embryonic structure. In one or 

 two instances, however, the adult structure begins with a small 

 varix. It appears that a suggestion made by the writer in a 

 previous paper (19) applies particularly to the species of Lotoi'ium, 

 and that none of them have left a conchological record of the 

 nepionic stage. It might have been inferred that the protoconch 

 had been deposited inside an original corneous one. Judging by 

 those species which I have been able to study, the whole shell is 

 cast inside its epidermal coating. After a rest-period the epidermis 

 grows very quickly and extends beyond the shell (the writer has 

 seen as much as half an inch overhanging, with the merest 

 " stiffening " of lime inside it), and inside this the shell is 

 deposited. It may be worthy of note here that in Lotoriiim, at 

 least, a varix is indicative of a " period of growth " of the mollusc 

 rather than of a "period of rest" of the shell. After the 

 formation of a varix [the gutter which Reeve describes (I.e.)], 

 and while the shell anterior to the preceding varix is yet thin, 

 the mollusc does not fill the cavity nearly so much as when this 

 part of the shell is thickened. The shell is enlarged by periods, 

 faster than the mollusc grows, which while growing is employed 

 strengthening its shell, not enlarging it. Harris (15, p. xii.) speaks 

 of variation in the size of apices of the same species. Among 

 fossils the variation is plainly noticeable, but as far as my 

 experience goes, it is practically non-existent among recent species. 

 The following descriptions, like the figures on the plates, have 

 been arranged to show the perfect graduation from the tall apex 

 of L. exaratum to the very flat one of quoyi. The letter A 

 indicates that species so marked have been referred by Tryon to 

 Shnpulum; B indicates Gutturnium. It is worthy of note that 

 the Jii' St and last of the series are marked with a B. Contour is 



