UNIO 



consult the characters of the hinge, yet judging from the 

 cast of the inside which is very common, we find no dif- 

 ference between it and casts that we have made from the 

 inside of recent Uniones, but we do not feel ourselves 

 authorized to pronounce the shell published in Min. Con. 

 t. 153. (U. crassissimus) to be an Unio; for its hinge is far 

 from being characteristic, and it has not the compound 

 posterior muscular impression of that Genus; it agrees 

 more nearly with some of the Lamarckian CypricardicB : 

 at the same time, we must confess our doubts about the 

 probability of that Genus being ultiaiately adopted ; our 

 individual knowledge of it is too imperfect to support 

 any opinion that we may hitherto have formed upon the 

 subject; of one thing we are, however, certain that some 

 of the shells referred by Lamarck to Cypricardia, are de- 

 cidedly species of our Astarte, his Crassina. Our atten- 

 tion is drawn in the next place to Unio Listeri, hybridiiSy 

 concinnus and others, figured in Mineral Conchology,'' 

 and placed in the Oolitic series by Conybeare and Phillips ; 

 and here, in confirmation of some observations we find 

 recorded in Conybeare and Phillips's " Outlines of the 

 Geology of England and Wales," we have to remark 

 that these, along with U. crassiusculus, Min. Con. t. 185, 

 from the Crag, all want some of the principal distin- 

 guishing marks of the Unio, and judging even from their 

 hinges, we should certainly hesitate to place them with 

 Unio. We have nev^r seen any perfect specimen of the 

 6hell published as Unio, from the fresh Avater formation ; 

 but if we may be allowed to decide from such fragments 

 ^s we have examined, and from its geological position, 

 we should hardly feel a doubt upon the subject. Not- 

 withstanding, however, what has been advanced above, 

 we must still consider the existence either of Uniones or 

 jlnodontes, in any bed below the Chalk, except the Coal 

 measures, as exceedingly problematical. 



In our plates we have represented, as characteristic 

 of this Genus, and as specimens of the variety of forms of 

 several species. 



Fig. 1. The Unio oralis, Mya ovalis, Mont. bi)t united to Unio pictorum, by 

 I^amarck, 



2. Unio ambiguus, Nobis. Castalia ambii^ua, Lam. Wc have lately been 

 m fortunate as to possess several specimcus of this rare and valuable shell, for 

 wWck Lamarck only cites the collection of the Marquis de Drfce. 



