A NEW GASTEROPOD (FAM. EUOilPHALIDAE) FROM THE LOWER 

 MARINE SERIES OF NEW SOUTH WALES. 



By John Mitchell, late Principal of the Newcastle Technical College. 



(Plate XXXV.) 



[Read 28th June, 1922.] 



Platyschisma allandalensis, n.sp. (PL sxxv.) 



Spec, chars. — Trochiform, large; spire consists of four whorls, first two de- 

 pressed and convolved so as to be subdiseoidal, penultimate and ultimate rapidly 

 increase in size and become spirate, the latter whorl relatively large. The trans- 

 verse growth lines are separated by rather wide, shallow, irregularly-spaced sulci, 

 and have a backward curve to the periphery; on the under side, the trend is re- 

 versed to the wide shallow umbilicus. As the shell reaches maturity the growth 

 lines and striae become almost straight between the whorl sutures and the peri- 

 phery. The outer lip has a shallow notch or gape, as in lanthina and in 

 Platyschisma oculus. Upper and under surfaces of the whorls are convex. The 

 mouth is very large, suboval or subconical and horizontal; the test was thin. 

 Diameter 4^ inches. 



06s. — The differences between Platyschisma oculus Sowerby, and the present 

 species are as follow: — The whorls of the latter are convex above and below, the 

 periodical growth lines are wider apart and more definite, the notch of the outer 

 lip is less deep, aperture horizontal instead of oblique as is the case in the former; 

 umbilicus shallower and the callosity or thickening of the lower lip less pro- 

 nounced, the body whorl increases in width more rapidly during its last stages 

 of growth than does that of Platyschisma {Keeneia f) oculus Sowerby or with 

 Keeneia platyschismoida Etheridge which I assume to be identical with Platy- 

 schisma oculus Sowerby, in part at least. 



In several respects this shell agrees with species of the present day lanthina, 

 but compared with them it was of gigantic size. It would appear to have been 

 a very rare shell in the Lower Marine Series at) AUandale, N.S.W., where it is 

 associated with Platyschisma oculus Sowerby, Eurydesma cord'atum, Aviculopecten 

 mitchelli Eth. and Dun and many other palaeopectens, etc. 



Locality and horizon. — Railway cutting near AUandale railway station. Lower 

 Marine Series, Permo-carboniferous. 



DESCRIPTION OF PLATE XXXV. 

 Platyschisma allandalensis, n.sp. 

 Upper figure- — View from the under side, showing the wide shallow umbiHcus, 

 and widely spaced growth Unes. The specimen is almost completely non-testiferous; 

 but otherwise nearly perfect. 



Lower figure. — View from above, showing the increasingly backward curve of 

 the growth lines as they approach the periphery, to form the gape in the outer 

 margin of the mouth, also mild convexity of the whorls, etc. 

 (Both figures two- thirds natural size.) 



