BRITISH SILURIAN BRACHIOPODA. 129 



portions of the valve. Just before reaching their furthest extension in front they give 

 ofiF a semicircular band or loop, vv^hich is directed upvi^ards towards the beak, and is exterior 

 to the spiral cones on their dorsal side. 



This genus has not been hitherto discovered in our British palaeozoic rocks, but it 

 will be desirable to give here a short description of the typical species. 



AnAZYGA JIECURVIROSTRA, Holl^ Sp. 



Ateypa recurtirostris, Hall. Pal. New York, vol. i, p. 140, pi. xxxiii, fig. 5, 1847. 

 Rhynchonella — Miller. The American Palaeozoic Fossils : A Catalogue of 



Genera and Species, &c., p. 127, 1877. 



" Elliptical, somewhat ovoid, very symmetrical ; breadth one fourth of an inch, length 

 a little greater. Dorsal [our ventral] valve with the middle elevated, regularly convex on 

 both sides ; the beak extending and gracefully incurved over the beak of the ventral [our 

 dorsal] valve, which is regularly convex with a slight longitudinal depression ; surface of 

 each valve marked by twenty-four simple longitudinal striae, which continue entirely to 

 the front " (Hall). 



Length 3|, width 3, depth 2\ lines. 



Obs. — The internal characters have been stated under the description of the genus, 

 and our knowledge of them is due to the Rev. N. Glass, who was able to develop the 

 spirals, attachments of principal lamellae to the hinge-plate, and connections of the 

 primary lamellae in a number of specimens kindly forwarded to him by Dr. G. J. 

 Hinde, 



Anazyga recurvirostra is a common shell in the Trenton Limestone of Ontario, m 

 Canada, and many of the specimens being filled with spar were peculiarly favorable for 

 Mr. Glass's operations. Prof. Hall states that it occurs in considerable numbers in a 

 compact greyish-blue bed of limestone near the centre of the Trenton Limestone near 

 Martinsburgh, Lewis County. 



We have not discovered this shell in our British Silurian Rocks ; and it is described in 

 this place in order to show another Hnk in the mode in which the primary lamellae are 

 connected in the AtyrpidcB. 



Prof. Hall does not describe the spirals or their attachments in this small species ; 

 but, singularly, in one of his figures (fig. I) of ^' Zijgospira modesta^^ he represents the 

 band or loop situated as it is in the shell under description. 



