^ GILBERT C. BOURNE. 



by the absence of spiral sculpture, and by the remarkable 

 solidity of the shell. He further asserted that his new genus 

 cannot, because of the above-mentioned differences, be in- 

 cluded among the Scissurellidte, and suggested that it is a 

 member of the Fissurellidfe in which development has been 

 arrested, so that the larval characters of the shell have 

 persisted in adult life. Hedley was evidently unacquainted 

 with Pelseneer's (12) memoir, containing an account of the 

 anatomy of this very species and of Scissurella costata, 

 which, brief as it is, leaves no doubt that the New Zealand 

 and the Mediterranean species are members of the same 

 family, but at the same time discloses so many anatomical as 

 Avell as conchological differences that they may well be placed 

 in different genera. After some consideration I am of the 

 opinion that Hedley's genus should stand, because the New 

 Zealand species, in addition to the conchological characters 

 enumerated above, differs from the Mediterranean species in 

 the following particulars: (1) In the shape of the radular 

 teeth. (2) In the shape of the foot, which is long and 

 narrow in S. costata and S. crispata, but short and 

 broad in Incisura ly tteltonensis. (3) In the absence of 

 cirrhi below the epipodial tentacles in Incisura. (4) The 

 greater development of the right columellar muscle, and the 

 more symmetrical disposition of the mantle in Incisura. In 

 its general anatomical features Incisura bears much the 

 same relation to Scissurella as Septaria bears to Paranerita 

 among the Neritidge. The systematic position of the Scissu- 

 rellida3 will more conveniently be discussed at the end of 

 this paper. 



Scissurella is placed by most authors among the Pleuro- 

 tomariidas, though a few recognise the Scissurellidee as a 

 separate but closely allied family. A full description of its 

 anatomy is therefore much to be desired, but the accounts 

 that have hitherto been published are insufficient. Vayssiere 

 (18) has given a short and, as far as it goes, a good account 

 of the external features of S. costata var. l^vigata, and 

 has figured and described the radula and jaws of this species. 



