FOSSIL LAMP-SHELLS. 231 



found adhering like limpets, by the entire surface of 

 the ventral valves, to other fossils. This family has 

 had a wonderfully long range in geological time, for 

 species belonging to it are not uncommon in the 

 Silurian rocks, and the genus has lived on ever since 

 into our own time, and is still to be found in British 

 seas, particularly in the marine lochs of Western 

 Scotland. 



The valves of Strophomena — abundant in the 

 Silurian rocks — are semicircular in shape, and the 

 two valves vary, being sometimes flat or concave or 

 convex. It is the type of a family of Brachiopods 

 to which the well-known genera Orthis^ Leptcena^ 

 StrepiorhychuSy etc., belong. 



The Prodiictus family is a very important and 

 a very interesting one. These fossils usually occur in 

 great specific abundance, so that if we meet with one 

 or two individuals we may expect to find others. 

 Indeed, the living Brachiopods are still distinguished 

 by their social or gregarious habits. Where they do 

 occur, they live in abundance. One of the pleasantest 

 rewards of the dredger in Oban Bay and there- 

 abouts is to bring up a clinker with half a dozen 

 living Terebratiilina capiU-serpentis. What a sensa- 

 tion it is to see in the flesh a representative of 

 one of the oldest and most continuously unbroken 

 families of the globe ! It is like raising a ghost 

 unawares. One of the best-known of living Bra- 

 chiopods is the Australian Waldheimia Ati sir alls. We 



