84 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
From these quotations it is evident that the Tilestone was regarded 
by Murchison as the upper member of the Silurian system as he denned 
it in 1854 and as it occurred in his typical sections. 
The writer's attention was first attracted to the possible equivalency 
of the Chapman sandstone and Tilestone of Murchison (-= Downton 
sandstone and Ledbury shale) by noting* that Leptwna lata of the list in 
The Silurian System is a true chonetes and closely resembles some of 
the specimens from Chapman. On studying up the definitions and 
synonymy of the species, it became evident that Davidson, who iden- 
tified Lej)twna lata von Buch with Chonetes striatella Dalman, in doing 
so was following DeKoninck. In quoting synomony, however, he 
excludes Sowerby's fig. 13 of PL V, which, as figured, presents the 
flatness characteristic of the species occurring in the Chapman sandstone. 
The chonetes (No. M 248) of the Chapman sandstone agree with 
HalPs C. nova-seotica * in size and form, and from descriptions it seems 
that the small specimens referred to C canadensis by Billings, 2 having 
the proportions of C. melonica, are identical with Hall's species C. nova- 
scotica. There is also a specimen (No. M 250) (the writer originally 
referred it to Orthothetes, the hinge and beak being absent) which 
upon examination is found to present the typical characters of Chonetes 
canadensis Bill., so far as they are visible. Dawson states that "the 
new species Chonetes nova-scotica is very characteristic of the upper 
member" [of the Arisaig section]. 3 Hall compared the species with 
U C. comutaoi the Clinton group of New York,"* but the Clinton 
species is much smaller than even the smallest specimens in the Chap- 
man sandstone. Billings, in describing the chonetes of the Gaspe 
series, calls his more gibbous form Chonetes melonica, and he compares 
this with C. striatella of Dalman, but finds it distinct (p. 16). Cho- 
netes canadensis Billings differs from the description of C. melonica in 
being nearly flat. Billings remarks, however, "Small specimens of 
this species [ C. canadensis] have nearly the proportion of C melonica, 
but are always nearly flat, while those of the latter are always more 
convex" (p. 18). 2 From a study of the descriptions it is evident that 
these "small specimens," referred by Billings to his species C cana- 
densis, are identical with the form described by Hall as C. nova-scotica, 
thus linking together the chonetes of the transition beds of the Gaspe 
section, formation D of the Upper Arisaig of Nova Scotia, and the* 
Chapman sandstone. 
Although the writer finds no description of the specimens referred by 
Sowerby to the species Zeptwna lata von Buch, the figure so labeled on 
PI. V certainly appears as if nearly flat. Even were this not the case 
(which an examination of the type specimens would demonstrate), the 
fact that we have in the Gaspe series both fully gibbous and flat forms, 
1 Canadian Nat. and Geol., Vol. V, p. 144, fig. 2. 3 Canadian Nat. and Geol., Vol. V, p. 137. 
2 Palaeozoic Fossils, Vol. II, Pt. I, p. 18. 4 Op. cit., p. 145. 
