228 GASTROPODA. [Pectinibranchia. 



1. Diala subcarinata, Murdoch and Suter, 1906. Plate 13, fig. 21. 



Diala subcarinata, Murdoch and Suter, T.N.Z.I.. xxxviii, 1905 (1906), 292, 

 pi. 24, f. 29. 



Shell minute, subulate, smooth, narrowly perforate. Sculpture : 

 The longitudinals consist of minute growth-striae, with a few growth- 

 periods, subcostate in places. Colour porcellanous-white. Spire high, 

 slender, and tapering. Protoconch consists of about 2 smooth rounded 

 whorls, the second slightly swollen, the nucleus oblique. Whorls 7. 

 slightly rounded ; the antepenultimate whorl is indistinctly feebly 

 bicarinate ; this is better defined upon the next whorl, especially the 

 superior angle which forms the subtabular sutural shelf ; upon the 

 last 4 or 5 feeble carinpe, 3 of which are above the aperture ; base 

 rounded. Suture deep. Aperture vertical, subtriangular. Outer lip 

 sharp, regularly curved, effuse, and angled at the junction with the 

 basal extension of the columella, producing a small spout-like canal. 

 Inner lip forming a narrow thin callosity on the pillar, which is sub- 

 vertical and slightly sinuated ; a thin callus extends above over the 

 body to the outer lip. Umbilicus very narrow, open. Operculum 

 unknown. 



Diameter, 1-04 mm. ; height, 2-9 mm. 



Type in the Dominion Museum, Wellington. 



Hab. Off Great Barrier Island, in 110 fathoms. 



A single empty shell was obtained. 



Fam. OMALOGYRID^EI, Sars. 



Animal having the body flattened, ciliated in front, no cephalic 

 tentacles; eyes sessile. Radula having the formula 1+1+1, the 

 central tooth with a quandrangular base with a large cusp, imbricated, 

 one series on the other ; a lateral transverse plate replaces the lateral 

 and marginal teeth. 



Shell planorbiform, spire involute, mouth clasping both sides of 

 the periphery ; operculum corneous, few-whorled, nucleus central. 



The animals are very active, and feed on alg;r. 



Genus 1. OMALOGYRA, Jeffreys, 1860. 



Omalogyra, Jeffreys, J. de Conch., 1860. Type : 0. nitidissima, Forbes and 

 Hanley. Ammonicerina, Costa, 1861. Homalogyra, Jeffreys, 1867. 



Shell small, discoid, flat, paucispiral ; whorls usually more or 

 less angled ; aperture orbicular ; peristome continuous ; operculum 

 circular. 



Distribution. Europe, Greenland, South Africa, and New Zealand. 



Remarks. The external characters of the animal and its dentition 

 are peculiar, and its systematic position is uncertain. 



KEY TO SPECIES. 

 a. Last whorl smooth, convex . . . . . . . . fusca. 



aa. Last whorl bicarinate . . bicarinata. 



