LOWER PALAEOZOIC GASTEROPODA — ETHERIDGE. 
75 
Genus Trochonema, Salter , 1859. 
(Canadian Organic Remains, 1859, Dec. 1, p. 24). 
Trochonema etiieridgei, Johnston . 
PI. xvi., Figs. 5 and G. 
Trochonema etheridgei , Johnston, Geol. Tas., 1888, t. 5, 1'. 13 
and 14. 
Sp. char . — Shell turbinate, of five or six acutely keeled and 
angular whorls, the principal keel occupying the periphery of 
each whorl ; on the anti-penultimate whorl there are three keels, 
the first small and thread-like bordering the upper suture, the 
surface thence to the second keel being tabulate or fiat, from the 
latter to the principal keel slightly oblique and concave, and 
thence to the lower suture the surface is straight- walled ; the pen- 
ultimate whorl possesses four keels besides the peripheral, the 
three upper arranged as in the anti-penultimate, whilst between 
the third and fourth the surface is again straight- walled ; the 
body whorl (somewhat hidden in matrix) probably possessed four 
also, the peripheral keel being strong and prominent. Sutures 
excavated. Mouth almost rhomboidal ; outer lip strongly angled 
at the peripheral keel, rounded below ; inner lip possibly straight. 
Umbilicus distinct. Sculpture consisting of oblique sub-imbricat- 
ing growth lamella.!, faintly varicose along the peripheral keel, and 
becoming much stronger and rugose towards the mouth on the 
body whorl. 
Obs . — This well marked shell was figured but not described by 
Mr. Johnston. In his plate explanation the author remarks that 
T. etheridgei is allied to T. tricarinata , Meek,* of the Oorniferous 
Group of North America. T. tricarinata , Meek, should be known 
as Ty meekianum , Miller. f The present shell is readily dis- 
tinguished from T. montgomerii , mihi, by its much more turbinate 
form, and different arrangement of the spiral keels and sculpture. 
Loc. and Horizon . — Gordon River, West Tasmania. Gordon 
River Limestone, Lower Silurian. 
Trochonema montgomerii, Eth^ fd. 
Eunema montgomerii , Eth., fil., Ann. Rep. Secy, for Mines Tas. 
for 1895-6 (1896), p. xlvii., pi. f. 21 and 22. 
Obs . — Since the publication of this species, further examples 
have been received from the Tasmanian Museum, one with an 
umbilicus exposed. This will necessitate its removal from Eunema 
to Trochonema. The following additional features may be noted : 
* Ohio Geol. Report, Pal. I., 1873, p. 218, t. 19, f. 5 a and b. 
f N. American Geol. and Pal., 1889, p. 428. 
