314 MISS MCDONALD AXD DE. TRUEMAX OjS^ [yoI. Ixxvii, 



luentecl by four spirals crossed by strong axials bearing low noclu- 

 lations at each intersection. The oral margin in the majoritj^ of 

 the specimens examined is slightly angular anteriorh^. 



Development (see fig. 4c). — The apex is preserved, and is 

 smooth for about one volution ; the next \vhorl is ornamented by 

 a single primary spiral occupying a more or less anterior position, 

 and on the next whorl a second primary spiral is added above the 

 first. Strong axial ornament appears on the succeeding whorl, 

 and persists throughout ; an extra spiral is intercalated in the 

 whorl following, and later (on the sixth whorl) a fourth spiral is 

 added. The ornamentation found on the sixth whorl is continued, 

 unchanged Texcept for a greater curve of the axials) until the last 

 whorl, which in our specimens is somewhat pupoid. 



This species has probably arisen from species of the JProceritJiiuin 

 ogerieni type by acceleration of the ornament, including the addi- 

 tion of a fourth spiral, and the loss of the flattened form of whorl 

 associated with the increase in strength of the middle spirals. 



Locality and liorizon. — Our specimens are from the Lower 

 Lias (^jamesoiii zone) in a railway-cutting at Toddington, near 

 Winchcombe, Grloucester (Mr. L. Kichardson's collection, L.Gr. 19). 

 Tate's holotvpe is also recorded from \\\e jamesoni zone^ Cheltenham 

 (20, p. 406). 



PEOCERiTHirM DAYi (Tate). 



Ceritliiinn dayi Tute (22, p. 7). 



Lectotype (chosen from Tate's specimens) : Museum of Practical Geology, 

 Jermyn Street, London, Xo. 7936. 



Apparently this species is closely related to the foregoing ; it 

 diffei-s, however, in the slightly stouter form of shell ; in the more 

 convex whorls ; in the less pronounced axials ; and in the number 

 and arrangement of the spirals, which are not equally spaced, the 

 three central (secondary) threads being closer together, and sepa- 

 rated b}" a wider interval froiu the two primaries. The aperture 

 has a slisrht sinuositv anteriorlv. 



L o c a 1 i t V and h o r i z o n . — Tate's specimens are from the 

 ' Middle Liis ' of Down Cliff. 



Peocemthium eaeicostati (Tate). 



Ceritlimm raricostati Tate (22, p. 8). 



Dimensions of holotype. 



LetHjth Breadth. Length of spire, 



{estimated). ^ -^ ^ 



5"3 mm. 41 per cent 68 per cent. 



Holotype : A specimen in the Tate Collection, Museum of Practical Geology, 

 Jermyn Street; London, No. 7962. 



This species has slightly convex whorls ornamented b}' stout 

 axial ribs and finer spirals ; on the later whorls these are about 

 eight in number. The network formed is oblong, owing to the 



Spiral 



Stittiral 



angle. 



angle. 



25° 



113° 



