202 



The characters and classification of the shells of this 

 family are not, however, yet determined : with the hope, 

 therefore, of leading to more decisive information respecting 

 these points, the structure of the hinge, as existing in a 

 shell bearing the external appearance of one of this family 

 from the mountain limestone of Shropshire, with which the 

 writer was favoured by the Rev. Mr. Hallifax, of Standish, 

 in Gloucestershire, is shewn, PL ix. fig. 9. 



Magas. An inequivalved, equilateral bivalve ; one valve 

 with an angular sinus along an incurved beak ; line of the 

 hinge, and back of the other valve, straight, with two pro- 

 jections near the middle. A partial longitudinal septum, 

 with appendages, are attached to the hinge within. Fossil. 

 PI. vii. fig. 14. 



Spirifer. An equilateral, inequivalved bivalve ; the 

 valves beaked : one valve with a large angular sinus along 

 the inside of the beak ; hinge transverse, long, and straight ; 

 two spirally-coiled tubular appendages nearly filling the shell. 

 Recent. PL vii. fig. 15. 



Astarte. Suborbicular or transverse ; ligament exter- 

 nal ; lunette on the posterior side ; two diverging teeth near 

 the beak. Fossil. PL viii. fig. 1. 



Inoceramus. An inequivalved, inequilateral bivalve, 

 slightly eared ; hinge formed of alternate ridges and furrows 

 on the margin of the eared part ; the substance of the shell 

 spathose, vertically striated. Fossil. PL viii. fig. 23.* 



Pentamerus. An equal-sided, inequivalved bivalve ; one 

 valve divided by a longitudinal, internal septum into two 

 parts ; the other, by two septa, into three parts or valves ; 

 the beaks incurved, imperforate. Fossil. PL x. fig. 7. 



* I have placed this shell among those, for the name and de- 

 scription of which, I believe, we are indebted to Mr. Sowerby, 

 although I have not yet been able to ascertain in what work his 

 account of the genus is to be found. 



