23 



that present unmistakeable pattern- markings, evidently derived from 

 the original colouring. They are 



Pleurotomaria carinata and conica, showing wavy blotches, resem- 

 bling the colouring of many recent Trochidte. 



An undescribed Trochus, showing a spiral band of colour. 



Metoptoma pileus, and 



Patella ? retrorsa, both with radiating stripes, such as are pre- 

 sented by numerous existing Patellidae. 



Natica plicistria, with broad mottled bands. 



Aviculo-pecten, a large unnamed species, with spotty markings on 

 the ribs in the manner of many existing Pectines. 



Aviculo-pecten sublobatus, Ph. ? Beautifully marked with radiating, 

 well-defined stripes, varying in each individual, and resembling the 

 patterns presented by those recent Avicules that inhabit shallows 

 and moderate depths. 



Aviculo-pecten intercostatus and elongatus also exhibit markings. 



Spirifer decorus and Or this resupinata, show fine radiating white 

 lines. 



Terebratula hastata, with radiating stripes. 



The analogy of any existing forms that can be compared with 

 those enumerated, would lead to the conclusion that the markings 

 in these instances are characteristic of mollusks living in a less 

 depth of water than 50 fathoms. In the case of the Terebratula, 

 which belongs to a genus the majority of whose living representa- 

 tives inhabit deep water, it may be noticed that all the living spe- 

 cies exhibiting striped shells are exceptions to the rule, and come 

 from shallow water. 



There are many circumstances which warrant us to suspect that 

 the carboniferous mountain limestone of most regions was a deposit 

 in shallow water. The facts now adduced materially strengthen 

 this inference. 



In the British Museum there is a beautifully spotted example of a 

 Devonian Terebratula, brought by Sir John Richardson from Boreal 

 America. 



Specimens of the Turbo rupestris, from the Lower Silurian Lime- 

 stone of the Chair of Kildare near Dublin, exhibit appearances that 

 seem to indicate spiral bands of colour. 



