Omalogyra.} GASTROPODA. 229 



1. Omalogyra fusca, Suter, 1908. Plate 13, fig. 22. 



Omalogyra fusca, Suter, P. Mai. S., viii, 33, pi. 3, f. 3(i. 



Shell minute, planorbiform, thin and fragile, slightly shining. 

 Sculpture consisting of very fine microscopic spiral striae, faintly re- 

 ticulated by growth-lines. Colour fuscous, with a few white radiate 

 streaks and irregularly scattered spots. Spire depressed. Protoconch 

 of 1 whorl, distinctly marked off from the next volution, spirally 

 striate. Whorls 2f , rather rapidly increasing, convex ; base concave. 

 Suture deep. Aperture circular. Peristome sharp, straight, slightly 

 discontinuous through the intervening parietal wall. Operculum un- 

 known. 



Diameter, 1 mm. ; height, 0-3 mm. 



Animal unknown. 



Type in my collection. 



Hob. Lyttelton Harbour, on seaweeds (H. S.). 



2. Omalogyra bicarinata, Suter, 1908. Plate 14, fig. 1. 



Omalogyra bicarinata, Suter, P. Mai. S., viii, 33, pi. 3, f. 37, 37a. 



Shell minute, discoidal, thin, not shining. Sculpture consists of 

 2 fine keels only, 1 above and 1 below the periphery. Colour white. 

 Spire depressed. Protoconch of 1 smooth whorl, marked off from the 

 next. Whorls 2J, rather rapidly increasing, flattened above and below, 

 convex at the periphery, bicarinate ; base slightly concave. Suture 

 canaliculate. Aperture, subquadrate. Peristome continuous, thin, and 

 straight. Operculum unknown. 



Diameter, 1-5 mm. ; height, 0-5 mm. 



Animal unknown. 



Type in my collection. 



Hob. Snares, in 50 fathoms (Captain Bollons). 



Fam. HYDROBIID^S, Fischer. 



Animal having a long rostrum ; tentacles elongated, with the 

 eyes at their outer bases. Ctenidium monopectinate ; sexes separate ; 

 the intromittant organ distant from the right tentacle, and generally 

 appendiculated ; one otolith in each otocyst. Jaws are usually pre- 

 sent. Formula of teeth of radula 2+1 + 1+1 + 2 ; the central tooth 

 mostly with basal denticulations. 



Shell with a prominent spire, turbinate or turriculate ; peristome 

 continuous ; operculum variable, horny or calcareous, concentric, 

 spiral or subspiral. 



The Hydrobiidce are small oviparous molluscs, living in fresh or 

 brackish water, some of them even, though branchiferous, out of the 

 water. 



Subfam. LITHOGLYPHIN^E. 



Foot simple ; central tooth of radula with basal denticulations ; 

 intromittant organ simple or bifurcate ; operculum corneous, spira 

 or subspiral. 



