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 Limea 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 Mans. 



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 Lima 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 opening and rapidly 

 closing or flapping their valves. The animal of Lima /dans 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 lamellae ; 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 5^ 

 inches in height and 4j long (ewcavafa, Chenm.), 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 Tertiad.es are somewhat scantily supplied. - 



1. Lima compta, S. Wood. Tab. XI, fig. 5. 



Spec. Char. L. testa tenui obovatd, valde obliqiid, subdepressd, inaquilaterali ; striata 

 vel cost/data, striis vet costulis numerosis, angustis, regularibits, acutis, scabris ; auriculis 

 magnis aquatibus ; cardine angusto, recto, simplici; umbonibus acutis, subpromenentibus. 



Shell thin, obovate, very oblique, somewhat depressed, inequilateral, striated or 

 costulated, striae 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 [Edwards). 



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 striae, and these are 

 numerous and regular. It somewhat resembles L. tenuis, Desh. (An. sans Vert, du 

 Bassin de Par., t. ii, p. 67, pi. lxxviii, 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. 



