444 GASTEROPODA OF THE INFERIOR OOLITE. 



possibly also of the higher parts of that zone. I have one specimen from 

 Shotwell, which in all respects corresponds with d'Orbigny's figure. The 

 specimen figured in the accompanying plate (PL XL, fig. 3) is between this 

 extremely smooth form and the ordinary PL plicopunctata. 



385. Pleukotomabia trapeza, sp. nov. Plate XL, figs, ha, hb. 



Description : 



Height . . . . .35 mm. 



Basal diameter . . . .44 mm. 



Spiral angle ..... 95°. 



Shell trochiform, subtabulate, slightly umbilicated. Spire regular, with 

 sharp apex. Whorls (seven) angular, and increasing by steps; the posterior area 

 has a moderate slope, whilst the anterior area (below the sinus-band) is almost 

 perpendicular, and constitutes a broad costated girdle round each whorl; sutures 

 close. The spiral system is overpowered by strong radial costse, which are 

 oblique above the sinus-band and axial below. 



The sinus-band is narrow and prominent, being situated mesially at the angle 

 of the whorl; owing to its prominence the ornaments seem worn. The body- 

 whorl is large and bluntly angular at the periphery, so as to be slightly 

 biangular Base very convex, with spiral ornamentation stronger than the 

 radial ; umbilicus small. Aperture subquadrate 



Relations and Distribution. — Intermediate forms between this and the larger 

 varieties of PL plicopunctata may be noted, and yet there is a tolerably sudden 

 jump at last ; whilst in the narrowing of the spiral angle there is a sort of return 

 to PL granulata of the lower horizon. Still I do not doubt that this is a kind of 

 offshoot from the common "granulate" Pleurotomaria of the P 'ark ins on i- zone 

 (i. e. PL plicopunctata). Moreover it is of importance with reference to the 

 occurrence of a tabulate form connected with the Granulatas on higher horizons, 

 such as PL granulata, Lycett, of the Scarborough Cornbrash, and even PL 

 Munsteri, Rom. (PL filigrana, Deslongch.), of the Lower Corallian. See page 440 

 with reference to Morris' identification of PL granulata on different horizons. 



PL trapeza is found at Burton Bradstock, and may be expected to occur at 

 Broadwinsor, and other localities of the Parlcinsoni-zone. 



