308 ON LEAIA MITCHELLI, 



Coal Measures. This hiatus has now been filled by Mr. Mitchell's 

 discovery at Charlestown, between Newcastle and Lake Macquarie, 

 of a Leaia, one of the most interesting genera of extinct Phyllopoda. 

 As a slight mark of appreciation of my friend's persevering efforts 

 in assisting to unravel the Paljeontology of N. S. Wales, I beg to 

 name the fossil Leaia Mitchelli. 



There are at present known eight forms of Leaia, species or 

 varieties,* as the case may be, extending from the Old Red Sand- 

 stone to the Permian in Geological time, with which the new 

 form will be compared. 



Leaia Mitchelli possesses transversely oblong carapace valves, 

 and as usual a more or less straight dorsal margin, angular at the 

 posterior end, but the anterior and ventral margins rounded. 

 The lateral carinse, two in number on each valve, increase in 

 thickness as the umbones are receded from, the anterior being 

 slightly curved, the posterior straight and diagonal, and sepa- 

 rating the valves into two unequal moieties. The concentric 

 laminae resemble those of other species. 



The type species, L. Leidyi, Lea, sp.,t is easily distinguished 

 from our form by its remarkably oblong-i'ectangular outline and 

 very scanty coarse concentric laminse, the direct anterior carinse, 

 and the sweep of the posterior ridges. The same remarks practi- 

 cally apply to the var. Williamsoniana, Jones, | from the Upper 

 Coal Measures of Manchester (Eng.). 



The second variety of the type species, var. Salteriana, Jones,§ 

 is more akin to L. Mitchelli, but the much shorter, wider and 

 more robust appearance of the former, and the emarginate 

 posterior end of the latter separate the two. Var. Salter iana 

 occurs in the Calciferous Sandstone Series of Fifeshire (Scot.). 



The Coal Measures of Saarbrilck, North Germany, have yielded 

 a Leaia, known as L. klieveriana, Goldenberg, in which there is a 



*See Etheridge, junr., Ann. Mag. Nat. Hist. 1879, iii. (5), p. 262; Etheridge, 



Woodward, and Jones, Brit. Assoc. Report for 1887 [1888], Pt. 1, p. 66. 



t Jones, Mon. Foss. Estheria3 (Pal. See), 1862, t. 5, f. 11 and 12. 



t Loc. cit., t. 1, f. 19 and 20. 



§ Jones, loc. cit., t. 1, f. 20. 



