PLEUROTOMARIA. 443 



Shell depressed, umbilicus deep and narrow. The spire is convex-depressed 

 with a flattened apex. Whorls (seven) flat and sloping, and ornamented with 

 oblique radial costge which are granulate at the points of intersection with the 

 spiral system. 



The sinus-band forms a uarrow, prominent ridge rather more than halfway 

 down ; owing to its prominence the spiral lines have not been well preserved, the 

 general appearance being that of a narrow, winding cord. The body-whorl is 

 relatively large, angular-compressed, and provided with a narrow, tuberculated 

 carina at the periphery ; base very convex and ornamented with a system of 

 flexuous radial costge, which spring from the margin of the small but deep 

 umbilicus. Aperture oval-depressed and oblique. 



Relations and Distribution'. — PL plicopunctata differs from PL granulata in 

 being more depressed, in its narrow but deep umbilicus, and especially in the 

 conspicuous radial ornamentation of the base. In both there is a tendency to 

 develop a tuberculated basal carina in the lower whorls of the spire, which adds 

 materially to the beauty of the shell. 



It is mainly a fossil of the Parlcinsoni-zcme, being especially abundant at 

 Burton Bradstock, Vitney Cross, &c, also in the Parkins oni-zone of Bradford 

 Abbas, Stoford, &c. There is considerable variety, with a tendency on the one 

 hand to pass into PL Palaemcm, and on the other into PI. trapeza. 



384. Pleujjotomaria Pal2emon, d'Orbigny, 1850. Plate XL, figs. 3 a, 3 b, 3 c. 



1850. Pleueoto uaria Palemon, d'Orbigny. Prod., i, p. 267. 



1854. — Terr. Jur., vol. ii, p. 468, pi. 



ccclxxx, figs. 7 — 11. 

 1873. Pal^mon, d'Orbigny. Tawney, Dundry Gasteropoda, 



p. 48 (40). 

 Syu. — granulata, vara, lentiformis and l^vigata, Deslong- 



champs. Vol. cit., p. 101, pi. xvi, figs. 4 and 5. 



Bibliography , 8fc. — It is pretty clear that Tawney, in quoting this species, was 

 disposed to include both PI. plicopunctata and PI. Palsemon under the latter 

 designation. Undoubtedly they are near relatives. 

 Description : 



Height . . . . .13 mm. 



Basal diameter . . . .35 mm. 



Spiral angle ..... 142°. 



The sunken spire, fineness of the lines, and the absence of coarse radial 



ornamentation in the base, are the principal features which separate PL Palemon 



from the preceding species. It is essentially a fossil of the Parlcins oni-zone, and 



58 



