35 



We have lately received from Van Diemen's Lanl three fine spe- 

 cimens of this shell, — two of them fully grown, and the other inter- 

 mediate in size between the young specimen we formerly possessed 

 and the adult state of the species. It may be observed that these 

 shells were all taken while the animals were growing ; the shells have 

 consequently the thin edge incident to that state of the animal, and 

 not the rounded thickened edge to the outer lip which the shell as- 

 sumes while it is in a state of rest after its former growths : though 

 probably the full size of the species, they are none of them what 

 conchologists generally call adult shells. But this form of the outer 

 lip is no proof of the adult state of the shell ; for the animal con- 

 stantly increases the size of the shell after such thickening and 

 periods of rest ; thus the thickening of the edge of the lip is only 

 a proof that the shell was taken and the animal destroyed while the 

 animal and shell were not increasing its size. 



The adult shell greatly resembles Scapha magnified in form and 

 colouring ; but the apex is much larger, irregular, with the apex of 

 the whorl on one side of the tip ; and the system of colouring is much 

 broader, and coarser in its character. 



Scapha mamilla. (Mollusca, PI. XLV.) 



Shell ovate ; nucleus very large, spire rather irregular, one- 

 coloured, orange, with the apex on one side ; the last whorl irregu- 

 larly markled with dark purple-brown lines having triangular pale 

 Spots, and with a subcentral and broad posterior sutural colourless 

 band. Pillar dark orange, with three oblique plaits. Throat 

 yellow. 



This form of the nucleus is found in another species of the genus 

 Scapha, but not in such a highly developed state, viz. in Scapha 

 fusiformis, also inhabiting Van Diemen's Land ; and it is also found 

 in the genus Fulgoraia. 



Several conchologists, for example the Messrs. Adams, have sup- 

 posed that this shell, on account of the size of the nucleus, ought to 

 be referred to the genus Cymbium, which is characterized by having 

 an irregular callous tip to the nucleus ; but if the nucleus of V. ma- 

 milla is properly examined, it will be found that it is distinctly 

 spiral, but has the apex of the first whorl of the nucleus excentric 

 or bent on one side ; and this is not very uncommon in several 

 species of Chrysostoma and Fusus, &c. 



The species of Scapha may be thus divided, according to the form 

 and surface of the whole of the nucleus :— 



I. Spire of nucleus regular, with a central apex. 

 a. Nucleus large ; ivhorls cremilated near the suture. 



S. vespertilio. 

 S. nivosa. 

 S. sophia. 



S. rutila. 



S. magnifica. 



