APPENDIX. 



LEAIA, Gen. Nov. 



I have proposed the above name as a generic denomination for certain peculiar, 

 quadrate, bivalved carapaces, occurring in the Coal-measures of Britain and the Lower Car- 

 boniferous red sandstone of Pennsylvania. I know nothing of their nature except that 

 they are small, thin, horny, brown, stiffly quadrate, symmetrical bodies, unlike Molluscan 

 shells, but possibly Crustacean and Phyllopodous. 



I have some specimens from the Upper Coal-measures of Ardwick, near Manchester 

 (collected by Prof. Williamson, P.R.S., several years since) ; and some from the Lower 

 Coal-measures of Pifeshire, collected by Mr. Salter, P.G.S., of the Geological Survey. Dr. 

 Isaac Lea described and figured, a few years ago, a similar fossil from the red sandstone 

 of Pennsylvania, and named it Cypricardia Leidyi. All these three are very much alike ; 

 but, on account of the obscurity of their relationship, and the distant places, geological and 

 topographical, of their occurrence, and making the most of their slight differences of contour, 

 I propose to keep them nominally distinct as Leaia Leidyi (PI. V, figs. 11, 12), L. Leidyi, 

 var. Williamsoniana (PI. I, figs. 19, 20), and L. Lcidyi, var. Salteriana (PL I, fig. 21). Dr. 

 I. Lea, of Philadelphia, being the first to notice and figure a specimen of this proposed 

 genus, I have distinguished it by a name commemorative of that well-known conchologist. 



The carapace-valves are oblong . truncate behind, with a slight curvature of outline ; 

 boldly rounded in front ; either straight or somewhat curved on the ventral border ; 

 straight on the dorsal edge ; a slight umbo takes the place of the antero-dorsal angle, from 

 wdience two conspicuous ridges (hollow within) pass along the surface of the valve ; one 

 directly across the valve to the antero-ventral angle ; the other, and longer one, passes 

 diagonally to the postero-ventral angle ; these ridges divide the convexity of the valves 

 into three, unequal, triangular, smooth, sloping areas ; the anterior space is the smallest 

 and nearly semicircular ; the middle one has its apex at the umbo and its base along the 



