48 EOCENE MOLLUSCA. 
is often a large distinct tooth in one valve, that interlocks into a depression in the other. 
M. Loven, in speaking of the animal of Zdmea Sarsii, says that the margin of the mantle 
is destitute of those tentacular filaments which form so rich an ornament to the animal of 
Lima hians. 
In the fossil genus Plagiostoma, there is a large gape on the rounded or siphonal 
region ; but this distinction is by no means a generic one, as the same character may be seen 
in shells of the living species of Zima proper. 
Some of the animals of this genus spin a byssus, and are said to be fixed; but others 
are able to swim with considerable vigour, like the Pectens, by openimg and rapidly 
closing or flapping their valves. The animal of Zima dians is a most beautiful object, 
sometimes of a deep crimson colour, with an orange-coloured mantle ; and it makes an 
artificial burrow with fragments of coral, shells, and sand. ‘The recent shell of this genus 
is always white, and, according to Dr. Carpenter; its outer layer consists of coarsely plicated, 
membranous lamellee ; the inner is perforated by minute tubuli, forming a complete network. 
This is wholly a marine genus, and the species are found in various parts of the world, 
from Norway to India, Australia, and the West Indies, and they present no special 
indication of climate. Mr. McAndrew obtained the largest living species, measuring 53 
inches in height and 44 long (evcavafa, Chemn.), on the coast of Finmark, and the European 
species possess a vertical range from 1 to 150 fathoms. A Permian fossil strongly 
resembles this genus, and it has continued through all the Secondary periods in large 
numbers ; the Tertiaries are somewhat scantily supplied. 
f 
1. Lima compra, S. Wood. Tab. XI, fig. 5. 
Spee. Char. L. testa tenui obovatd, valde obliqud, subdepressd, inequilaterali ; striata 
vel costulatd, striis vel costulis numerosts, angustis, regularibus, acutis, scabris; auriculis 
magnis aqualibus ; cardine angusto, recto, simplici ; umbonibus acutis, subpromenentibus. 
Shell thin, obovate, very oblique, somewhat depressed, inequilateral, striated or 
costulated, strie or riblets numerous, narrow, sharp, regular, and rough ; auricles large 
and equal; hinge-line straight, with pointed and rather prominent beaks. 
Longest diameter, ~ of an inch. 
Locality. Barton (Hdwards). 
One specimen is all that I have seen, and this is not quite perfect; but it differs 
from any species I am acquainted with, as indicated by the lines of growth. I believe it to 
be distinct. The entire surface of this shell is covered with radiating striz, and these are 
numerous and regular. It somewhat resembles Z. ¢enwis, Desh. (An. sans Vert. du 
Bassin de Par., t. 1, p. 67, pl. Ixxviu, figs. 20—22); but it is more oblique than that 
figure, having the umbo incurved, and not so prominent ; there is also, seemingly, a deeper 
sinuation under the auricle in the siphonilateral margin, and the rays upon our shell are 
more numerous and less regular. 
