74 EECORDS OF THE AUSTRALIAN MUSEUM. 



below the level of the body whorl, which is traversed on its outer 

 angle by a keel, without nodes, crenulations or echinations, but 

 variable in its degree of prominence and acuteness, on the inner 

 side of the keel the surface of the whorl slopes rapidly away to 

 the suture, with immediately above it a second feeble obtuse keel; 

 on the under side the surface of the body whorl is either gently 

 rounded or flattened, but the inner whorls rounded only ; umbilicus 

 telescopic, but most of the whorls visible ; back in no way concave 

 l)eneath the keel of the body whorl, but rounded and broadening 

 towards the mouth, the surface loosing much of its convexity. 

 Mouth generally rounded, but slightly insinuated at the keel, and 

 more so along the sutural margin, the upper margin, in other words, 

 retreating towards the shallow notch or insinuation referred to, 

 and the lower edge advancing and insinuated. Sculpture of the 

 upper sui'face consists of fine obliquely retreating lyrulpe on the 

 inner half of each whorl, and similar advancing lyrulse on the 

 outer half, giving a faintly V-shaped figure, but on the wide 

 back these lyrulte become more directly transverse ; on the under 

 surface the lyrulje descril)e a sigmoidal curve, becoming much 

 coarser and sub-laminar towards the mouth, the sharpest portion 

 of the curve being immediately above the suture at the obtuse 

 feeble keel. 



Ohs. — Under the name of StraparoUus tasinaiiicus, I feel con- 

 vinced Mr. R. M. Johnston has included two perfectly distinct 

 shells. His figs. 1 and la. represent a Rajohistoma that may be 

 known as Raphistoma tasmanicum, Johnston, sp., whilst fig. 7, 

 the subject of the present I'emarks, appears to me to be a Helico- 

 tonia, and I therefore propose for it the name of H. johnstoni. 

 The specimen now figured was received in a collection of fossils 

 forwarded from the Tasmanian Museum. PI. xv.. Fig. 6, repre- 

 sents the upper side, corresponding to Johnston's fig. 7, whilst 

 our PI. XV., Fig. 7, is that of the under or umbilical side of the same 

 specimen. I am puzzled how to distinguish this from another 

 shell that Mr. Johnston has figured as Lituites, sp. indet.,* except 

 that in the latter the transverse laminae are too coarse for the lines 

 occurring on the under surface of Helicotoma johnstoni. 



In the faintly V-shaped outline of the sculpture on the upper 

 side, the apex of the V is at the keel of the body whorl, producing 

 a slight notch on the outer lip, after the manner of Helicotoma, 

 without in anyway simulating a true sinus. This reflection of the 

 sculpture lines and the presence of the notch distinguish this 

 shell at once from Polytropis, De Koninck. 



Loc. and Horizon. — Gordon River, West Tasmania. Gordon 

 River Limestone, Lower Silurian. 



* Johnston— Geol. Tas., 1888, t. 5, f. 8 and 10. 



