PRODUCTA. 



have been preferable to any other : our classical friends 

 inform us that this is incorrectly done by Sowerby^ in his 

 Mineral Conchology of Great Britain; by altering its 

 termination, one objection at least will be removed. We 

 would willingly have substituted a preferable name, had 

 any been suggested which would have unexceptionably 

 characterized the Genus. 



This singular bivalve is equilateral and inequivalve ; 

 one valve being generally convex, very rarely rather flat, 

 with its anterior edge rounded, very thin, turned down- 

 wards (or inwards), and produced into the form of an 

 irregular cylinder, and a little expanded towards its lower 

 edge ; the other valve is generally flat, or a little concave 

 on the outside, with its anterior margin turned backwards, 

 so that its inner side lies against the inside of the concave 

 valve. The cardinal or posterior margin is transverse, 

 straight and linear, and sometimes continued so far on 

 both sides as to render the shell subalate. We have never 

 seen the remains of any ligament, nor do we suppose 

 that when the animal was living its valves were united by 

 any. It is very seldom that the inside of either valve 

 has come under our observation, but in some casts, and 

 in a specimen of a flat valve from the Transition Lime- 

 stone of Dudley, there are indications of internal pro- 

 cesses near the hinge. The texture of the shell is exactly 

 like that of the other Brachiopoda ; it is granular within, 

 and frequently spinose on the external surface. 



The fossils of this Genus occur principally in the 

 Mountain Limestone; they are also found in the Transi- 

 tion Limestone of older date, and in the Steaschist* of 

 Snowdon, (see Phillips, in Annals of Philosophy,) as 

 well as in Magnesian Limestone at Breden, near Derby; 

 but in this latter they appear to be rare, as they are not 

 mentioned by Conybeare and Phillips. About 20 species 

 are figured in Mineral Conchology. 



Mr. Konig obligingly informs us that the names of 

 Polyginglymus and Pyxis have formerly been applied to 

 a species of this Genus : but vmfortunately both of these 

 names have been preoccupied. 



Fig. 1. Producta Martini. 



depressa, Nobis. 



' antiquata. 



* It would have been more correctly termed Steatoscfiist. 



