INCISUEA (sCTSSURELLA) LYTTELTONENSIS. 



On the Anatomy and Systematic Position of 

 Incisura (Scissurella) lytteltonensis. 



By 



Oilbert €. Bourne, 



Fellow of Merton College, Oxford, and Linacre Professor 

 of Comparative Anatomy. 



With Plates 1—5. 



•^ When Mr. Geoffrey W. Smith was in Tasmania in 1907-08 

 I asked him to collect for me any rare or remarkable speci- 

 mens of gastropod molluscs and preserve them in a form 

 suitable for anatomical and histological examination. Among 

 other forms Mr. Smith obtained for me^ through the kind 

 offices of Mr. C. Hedley, of the Australian Museum, Sidney, 

 a number of specimens of the little gastropod which is the 

 subject of the present memoir. They were preserved in 

 Perenyi's fluid, which of course dissolved the shells, but 

 except for the difficulty of stainiug always resulting from a 

 prolonged immersion in this reagent, the histological condition 

 of the specimens leaves little to be desired. 



Scissurella lytteltonensis was described in 1893 by 

 E. A. Smith (16), who noted certain differences between the 

 shell of this and other species of the genus Scissurella, but 

 evidently did not consider them of generic importance. In 

 1904 C. Hedley (8) recalled attention to these differences, 

 and founded the new genus Incisura for the reception of 

 the species which, he maintained, is marked off from all 

 other Scissurellidae as also from all Pleurotomariidae by the 

 brevity of the slit in the shell, by the absence of raised rims 

 or keels on either side of the slit, by the subterminal apex, 



VOL. 55, PART 1. NEW SERIES. 1 



