66 GASTEROPODA. EMARGINULA. 
conically depressed; concave within ; destitute of spiral 
convolutions, but with the vertex perforated, and directed 
towards the front of the shell: the perforation is subovate 
or nearly round; margin of the shell thickened around the 
inside, and generally crenulated ; muscular impression 
visible near the inner edge, all round, widest on the sides 
near the front ; outer surface striated, grooved, or radiated 
from the vertex to the margin, and generally decussated by 
lines of growth. 
Fissurella greca. Plate LV. figs. 18 and 24. Found in 
the Crag at Ipswich. 
This is 4 genus of marine shells, and consisting of nearly forty species. 
They inhabit the seas of every quarter of the globe; and one species is found 
on the British coasts. 
A few fossil species have been found in the marine formations above the 
chalk. 
Genus VIL. — SIPHO. — Brown. 
Generic Character. — Shell subconie, vertex reflected, 
and slightly spiral, with a small dorsal fissure near the apex, 
terminating interiorly by a rhombic funnel-shaped syphon; 
base ovate. 
Sipho clathrata. Plate IV. fig. 8. Found in the Oolite 
at Ancliffe. 
They inhabit the sea, and one species, the S. striata, has been found in the 
Clyde, and in a sub-fossil state, at Dalmuir, near Glasgow. 
Genus VIIT. — EMARGINULA. — Lamarck. 
Generic Character. — Shell conical, shield-shaped ; ver- 
tex inclined to the posterior extremity; anterior margin 
with a fissure, or notch ; internal cavity simple; anterior 
sides of the muscular impression interrupted, expanded, and 
not continued across the front. 
Emarginula tricarinata. Plate IV. fig. 20. 
Sowerby has, in our opinion, most improperly reunited this genus and 
Parmophorus. Both genera have peculiarities of structure, by which they 
may at once be recognized, and consequently, the reunion must tend to con- 
found, rather than improve the arrangement. 
The species of Emarginule do not exceed four or five; they are marine 
shells, and inha!it the seas of almost all climates ; one ofthem, E. fissura, isa 
native of the British coasts. 
Fossil species are not plentiful, they occur in the Calcaire-grossier at 
Grignon, and other contemporaneous formations; also in the Crag of Essex, 
Norfolk, and Suffolk, and the Bath Oolite. 
