128 



SUPPLEMENT TO THE 



difference, that in Z. Anticostensis the upper part of the loop on either side, and the 

 attachments to the hinge-plate, are bent backwards 

 towards the ventral valve. This peculiarity will be seen 

 in the accompanying figures. 



In PI. XXII of my Silurian Monograph I figured, 

 but did not describe, a variety of Zygospira by the name 

 Atrypa {?) Headi, var. Anylica. Unfortunately our 

 English and Irish specimens are not generally found in a 

 good state of preservation, and consequently it was not 

 possible to work out their internal arrangements. Mr. 

 W. H. Baily has kindly again forwarded for my in- 

 spection some casts and impressions of the fossil in 

 the possession of the Geological Survey of Ireland, 

 which were collected from the Lower Silurian at 

 Externally they bear much resemblance to Z. A/iticon- 

 tiensis ; and to this species, and not to Z. Headi, I would, at any rate provisionally, 

 refer them. The specimens from the Caradoc of Moelydd, Shropshire, show the sinus in 

 the ventral valve as in AnticostieTisis (' Sil. Mon.,' PI. XXII, fig. 8 b and d), and are 

 exactly similar in shape to Billings' fig. 127. 



Zygospira Anticostiensis and its variety borealis seem to be very common in a grey- 

 coloured limestone in the Hudson-River formation, or what is more suitably termed the 

 Cincinnati group, near English Head, west end of Anticosti ; also on Lake St. John, on 

 the River Saguenay, as well as in other places ; and the Irish variety Anglica is equally 

 common at Grangegeeth. 



Zygospira Anticostiensis, Billings, sp. 



Fig. 1, showing spirals and loop, a, h : iu 

 fig. 2 a and b, are continuations of the loop 

 and primary lamella from a, b, in fig. 1 ; D, 

 dorsal ; T, ventral valves. Cincinnati 

 group, English Head, west end of Island 

 of Anticosti, Canada. Developed by the 

 Eev. N. Glass. 



Grangegeeth, County Meath. 



Genus — Anazyga, Dav., 1882. 



ava, upwards, t,hyov, a couuecting baud. Type Atrypa recurvirostra, 

 Hall. 



Shell small, longitudinally oval, and radiatedly striated. 

 The position of the spiral cones in the type is the same as 

 in Zygospira, the base of each spiral cone being obliquely 

 inclined towards the bottom and sides of the ventral valve. 

 There are about four coils in each spiral cone. The 

 primary stems of the spirals are attached to the hinge-plate 

 of the dorsal valve ; and, after extending parallel to each 

 other for a short distance, they bend at right angles abruptly 

 towards the lateral portions of the beak, and form two large curves facing the lateral 



'. recurvirostra, dorsal aspect, 

 showing spirals, attachment to the 

 liinge-plate, and loop. Trenton lime- 

 stone, Ontario, Canada. Developed by 

 the llev. N. Glass. 



