KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. N:0 (6. 79 
General Remarks on the Species of Microcystis. 
As Heptey (1912) remarks, the Queensland forms of the genus Microcystis 
have not been definitively distinguished. They are very uniformly shaped and diffi- 
cult to identify without types for comparison. In order to facilitate their identi- 
fication and to contribute to a better knowledge of the genus, I have undertaken a 
close examination of the above species, with the following results. 
Concerning the shell, M. marmorata is easily distinguished from all the others 
by its angulated periphery, as well as by its comparatively large size, 12 mm in 
diameter at 5*/s whorls. The colour is yellowish gray as in M. rustica, equal above 
Fig. 28. Genital organs of Microcystis fulvan. sp. a albumini- Fig. 29. Genital organs of Microcystis 
parous gland; d. dart sac; ep. epiphallus; g. hermaphrodite rustica Cox. fl. flagellum; p. penis; 
gland; p. penis; r. p. retractor penis; r. ¢. tentacular retractor; r. p, retractor penis, v. d. vas deferens. 
u. uterus; v. vagina. 
and below, and the umbilicus is furnished with a few dense oblique furrows, but not 
infringed by any columellar sinuation. 
The same yellowish or reddish gray colour is confined to M. rustica and M. 
responsivus; the latter is lighter above. Both have also spiral furrows entering the 
umbilicus and occupying a broader zone in M. rustica; a columellar sinuation is pre- 
sent in both, and the whorls are rounded. M. rustica is more elevated (height of 
shell > aperture breadth; in M. responsivus the height is — the aperture breadth). 
The outer lip is inserted at an acute angle to the body whorl in M. rustica and at 
nearly a right angle in M. responsivus; in the last-named the inferior aperture margin 
is slightly convexly projecting in the middle. There is only a slight difference in 
size: at 57/2 whorls M. rustica is 9.5, M. responsivus 10 mm in diameter. 
M. fulvua and M. kreffti differ from the three named species in their fulvous 
or orange colour, equal above and below. They have no columellar sinuation and 
