110 Frederick Chapvian : 



plates or dental lamellae are seen attached to the sides of the cardinal 

 area of the shell. A narrow slit-like depression, at the base of which 

 the foramen was situated, is seen in the upper third of the deltidial 

 area. Area on either side of the delthyrium transversely striate. 

 Anterior margin of the pedicle valve irregularly flexuose. Cardinal 

 extremities of valve blunt. Shell smooth, excepting for a few con- 

 'Centric, lamellar folds and the sharply plicate margins of the sinus, 

 the latter being deeply sulcate. 



Measurements. — Holotype : Length, 6 nun.; width, 9.75 mm.; 

 length of hinge area, 3.5 mm. 



Observafio?is. — The nearest related form to the above is James 

 Hall's C. hiplicata,^ a Lower Devonian species, which occurs in the 

 ■Corniferous Limestone (Upper Helderberg) of Michigan, and in the 

 Schoharie Grit of Schoharie, N. York (base of Upper Helderberg 

 'Group). 



The present species differs in its blunt cardinal extremities and 

 more deeply sunken sinus of the pedicle valve. 



Occurreyice. — Silurian (Yeringian). In brown mudstone at Rud- 

 •dock's Quarry, near Lilydale. Collected and presented by J. S. 

 'Green, Esq. 



Genus Spir'ifer, Sowerby. 

 Sjjirifer lih/daleiisis, sp. nov. Plate XI., figs. 17, 18. 



Description. — Shell referable to the .S'. sub-orb icularis type; that 

 is, " with sub-orbicular outline, broad, low and usually lateral 

 plications; the median plications are few and indistinct.''- Shell 

 almost equally convex, with rounded to salient cardinal extremities. 

 The pedicle valve is strongly curved towards the prominent beak ; 

 mesial sinus deeply excavate and feebly plicated, especially near 

 the anterior margin, the margins of the sinus more or less ridge- 

 like. The brachial valve bears a broad mesial fold, which is con- 

 spicuously, longitudinally striated. The general shell-surface is 

 finely striated by delicate radial lines, and the shell is irregularly 

 set off concentrically by a few lamellar growth-lines. Radial ribs 

 rounded and gently curved; tliey number from 8 to 10 on each side 

 of the fold and sinus. 



Mcdtiiirciiieiifs. — A Itrachial valve (coty])e) : Length (anterior 

 iii.iigiii to beak), 19.5 nun. ; widtli, .30.5 mm. .\ ventral valve 

 (cotyp(>): Lengtli, U mm.; width, 22 mm. 



1 See Hall and Clark, Pal. N. York, vol. viii., I'al. Hnuli., pt. ii., 1S9-1, pi. \xviii., fij>s 7-9. 



2 Hall arifl Clarke, Pal. N. York, vol. viii., I'al. Hr.icli., pt. ii., 1894, p. Hi. 



