84 CANADIAN MECRO-PAL^ONTOLOGY. 



is comparable with pi. xiii, fig. 3, from the same locality, namely Long 

 Point, Lake Winnipegosis. At first sight, pi. x, fig. 5, is not readily 

 diytinguishable from L. jahuliies (L. Josephiana) ; but it is fuller in 

 the antero-ventral outline. Indeed the specimens before us are not 

 only higher (deeper) in the antero-ventral moiety, but^ have less pos- 

 tero-dorsal slope, are not quite so convex, and show usually some slight 

 marginal rim. 



This is No. 9 of the series, and was collected at Long Point on the 

 east side of Lake Winnipegosis, by Mr. J. B. Tj^-rell in 1889. 



Other specimens collected by Mr. Tyrrell at the same time and 

 place, and more or less closely resembling fig. 5, but diifering in size, 

 are : 



No. 10 — Left valve Lengtli 



No. 11 — Left valve 



No. 13 — Right valve 



f - Left valve. — 



No. 14 (fig. 7)^ r:,;,' 



( —Right valve 



Mm. Mm. Mm. 



lOJ (hinge-line.. 5J) height.. 61 



5^ ( .. 4 ) ... 3i 



6 ( .. 3 ) ... 3 



7 ( .. H) ... 4-^ 



6^ ( .. 5 ) ... 4 



In this case also we have evidence of an old prototype, or analogous 

 predecessor, of a Silurian (Upper Silurian) species; both the older and 

 the newer representative form having approximate varieties, peculiar to 

 zones and localities. 



From the white, hard, thin-bedded limestone at the Grand Rapids, 

 another similar form occurs as casts, without any surface-marks, pi. 

 xii, fig. 8 (x4). Its shape is nearly that of pi. xii, fig. 15 (x3), and pi. 

 xiii, fig. 3, (x3), but its bareness, its poor dorsal angles, and the absence 

 of marginal rim, go far to distinguish it. This may be another variety 

 (egena) of Leperditia Hisingeri. 



13. Leperditia alta (?), Hall. 

 PI. 13, figs. 10, 11a, and lib. 



For the synonyms of and notes on this species, see Quart. Journ. 

 Geol. Soc, vol. xlvi, 1890, pp. 25-27. 



There is great apparent discordance in the figures and descriptions 

 of the specimens commonly referred to L. alta, and abundant in the 

 Schoharie Limestone (Lower Ilelderberg), of New York State. PI. xiii, 

 figs. 10 and 11 are from a slab of the limestone, and though regarded 

 as L, alta, they do not match any of the various published figures of 

 this species, which yet requires close critical examination. Both fig. 

 10 (the left and smaller valve), and fig. 11 (the right and larger valve) 



