358 THE DEVONIAN FOSSILS OF CANADA WEST. 
of the margin below. The greatest width (which is at mid-length, 
and nearly at right angles to the greatest length) is one inch and 
three quarters. Depth of both valves, at a little above the middle, 
one inch and a half. The umbones are elevated nearly half an inch 
above the hinge-line. The whole shell is pretty evenly convex, with 
a slight approach to a concave slope in front of the umbones. There 
appears to be an area, but our specimens do not shew it with sufficient 
clearness to warrant a positive opinion. 
This species 1s dedicated to the discoverer, W. G. Tomkins, Esq., 
C. E. St. Mary’s, Canada West. 
Locality and Formation.—Corniferous Limestone, St. Mary’s. 
Collector.—W. G. Tomkins. 
GasTEROPODA.—(Cuvier. ) 
We have in the Devonian Rocks of Canada West about 25 species 
of Gasteropoda of the genera Huomphalus, Straparollus. Murchisonia, 
Pleurotomaria, Loxonema, Macrocheilus, Platyostoma and Platyceras. 
Of these I shall only notice the following at present. 
EvompHatus De Cewr.—N. Sp. 
Fig. 131. Fig. 182. 
Fig. 181.—Huomphalus De Cewi.—A small specimen. 
Fig. 132.—View of the umbilicus. 
Description.—Shell from two to four inches in diameter ; whorls 
about three. Spire nearly flat or gently concave; umbilicus deeply 
concave. The upper side of the whorls is nearly flat, with an angular 
edge all round the margin, (in casts narrowly rounded). The outside 
of the whorls nearly at right angles to the upper, but inclining a 
little inwards and gently convex. On the lower side there is a narrow 
rounded edge all round, from which there is a nearly uniform concave 
slope into the deep sub-hemispherical umbilicus. 
