260 ON SOMK r.AND SHELLS COI.LKCTED IN QUEENSLAND, 



Microcystis rustica Pfeiffer. 

 (Plate viii., fig.4-2.) 



Helix inconspicua Forbes, Voy. Rattlesnake, ii., 1852, p. 379, 

 Pl.ii., {.3a, b, c (not Helix incons'picua C. B. Adams, Contrib. 

 Conch., iii , 1849, p. 37); Helix rustica Pfeiffer, 7iom. mut., Zeit. 

 fiir Malak., ix., July, 1852, p. 11 2; Helix impexa Reeve, nom. 

 mut., Conch. Icon., x., Oct. 1852, Pl.cxxx., f.795; Uelix crotali 

 Cox, nom. mut., Cat. Austr. Land Shells, 1864, p. 18; Helix 

 villaris Reeve, Conch. Icon., x., Sept. 1854, pl.cxcv., f.l375: Id., 

 Pfeiffer, Proc. Zool. Soc, 1854,(April Uth, 1855) p.H6. 



The group of Queensland land-shells to which this species 

 belongs, has been overloaded with names, and yet poorly differ- 

 entiated. Von Martens formed, for it, a group, Thalassia, with 

 Helix subrugata Pfr., for its type. This name was already 

 occupied in birds, so Gude has substituted Nitor.* The genus 

 Fretum Sykes, t appears to be near akin. The generic position 

 must depend on structural details not yet ascertained. 



In adult M. rustica, the left lip near its intersection is 

 thickened, expanded, and bent down over part of the umbilicus 

 (Plate viii., fig. 42). Guided by this feature, the species should 

 arrive at the genus Microcystina. But this character gradually 

 disappears in related ■ species; thus, in M. kreffti, the columella 

 springs more vertically from the insertion, but the fold of M. 

 I'ustica is represented by a thickening and a slight insinuation. 

 In other, especially in thinner species, the columella is as in the 

 immature M. rustica. Discai'ding, as unstable, the character of 

 the guttered columella, I have referred the species to Microcystis. 



From an island in Trinity Bay, near Cairns, Forbes figured 

 and described the fii'st known Australian species. Unfortunately 

 he selected, for it, a name already used for a West Indian snail 

 by C. B. Adams. Pfeiffer, Reeve, and Cox, each in turn offered 

 a new name in correction of the error. But Pfeiffer, only know- 

 ing the species by name, and receiving it from the same collector 



*(iude, Proc. Malac. Soc, ix., 1911, p.270. 



tSyke.s, Proc. Malac. Soc, iv., 1900. p. 1-IU. 



