ANIMALS. 165 



answered a similar purpose, — a conclusion powerfully supported by an examination 

 of Modiola vulgaris, in which the cartilage is internal, and attached to the surface 

 of an excavation in the thickness of both hinge-plates. Now it is not difficult to 

 comprehend how easily such a fulcrum could become modified into that of Edmondia, 

 by the inferior margin of each excavated surface becoming more and more projected 

 from the hinge-plate. A modification of this kind is instructively illustrated by the 

 cartilage fulcral plates, or spoon-shaped processes, in both valves of Mi/a truncata. 



It remains to be observed, that the cartilage-plates in Edmondia vary somewhat in 

 direction, according to species. In Edmondia unioniformis {Isocardia id., Phillips), and 

 Ed. Murchisoniana, they are closer to the surface of the umbonal cavities than in 

 E. sulcata} 



The wide space between the cartilage-plates of the present genus indicates that 

 the cartilage has been of considerable thickness ; but it does not appear to have been 

 much thicker than that of Modiola, Lutraria, and Mi/a. 



The anterior portion of the muscular system of Edmondia is somewhat peculiar. In 

 good casts of Edmondia sulcata there are four muscular impressions in front of the 

 umbone ; two large ones perpendicularly situated (the uppermost, which is half the 

 size of the lowest, is bounded posteriorly by a slightly elevated ridge), and other 

 two, which are very small, situated between and at right angles to the former. The 

 lowest of the large impressions may be safely referred to the anterior adductor muscle ; 

 while the uppermost, together with the two small ones, I am of opinion belonged to 

 the visceral or pedal muscles. The large size of the uppermost muscular impression 

 is seemingly indicative of the Mollusk having had a large foot, as is the case with 

 Unionida and some other families. 



Concluding from what is at present known, the existence of Edmondia appears to 

 have been confined to the close of the primary period ; as species are not yet known to 

 occur in any other than the Carboniferous and Permian formations. 



Edmondia Murchisoniana, King. Plate XIV, figs. 14, 15, 16, 17. 



Edmondia Murchisoniana, King. Catalogue, p. 10, 1848. 



— ELONGATA, Howse. Trans. T. N. F. C, vol. i, p. 243, 1848. 



i)^«yrao5^>.— ^Transversely oblong ; inequilateral ; rather tumid ; slightly wrinkled, 

 and finely striated parallel to the margins. Half an inch in width, and three eighths in 

 length. Valves with a rectilinear hinge-margin, obtusely rounded or somewhat squared 

 lateral extremities, and a flatly convex ventral margin. Cartila(/e-fulcra half the length 

 of the cardinal line ; strongly curving within the umbonal cavities ; with the free 

 margin of their anterior half deeply sinuated. 



1 The character of the cartilage fulcra of Edmondia is strikingly simulated by the posterior adductor 

 muscular plates of Teredo navalis ; and very singularly so by those of T. bipennata, in which they are 

 actually external, being elevated above the dorsal margin of the valves. 



