ADDENDA. 



A PORTION of the text of this Supplement passed through the hands of the printer long 

 prior to the execution of the plates ; and during this lengthened interval many additional 

 testacea were placed at the disposal of the author, including a considerable series from the 

 Forest Marble of the counties of Wilts, Somerset, and Dorset, which had recently been 

 disengaged from the investing matrix by the exertions of W.Walton, Esq., of Bath, 

 obtained by that gentleman, and by the late John Kilvert, Esq., of the same place. This 

 fine collection has yielded many new forms, and also some superior examples of others 

 that had previously been figured from specimens less suitable for the purpose ; advantage 

 has been taken of the opportunity thus afl'orded to give additional illustrations. The 

 descriptions of the more recently acquired fossils could not, therefore, for the most part, be 

 placed in their proper order, and necessarily form Addenda to the Supplement. 



Cerithium (?) HEMiciNCTUM, Lyc. Tab. XLI, fig. 17. 



Testa parva, elongata, anfractibus (7), valde conveccis, postice subplanis, laevigatis, 

 antice tricinctis, convexis, anfractu ultimo basi concentrice striato. Apertura et canali 

 ignota. 



Shell small, elongated ; volutions (7) very convex, their posterior portions oblique, 

 flattened and smooth, their anterior portions with three prominent encircling costge, the 

 sutures are deeply constricted ; the last volution has the base concentrically sulcated ; the 

 outer lip and the base are imperfect ; the genus, therefore, is somewhat uncertain ; there 

 are some traces of an umbilical opening at the base of the columella. 



Geological Position and Locality. The Forest Marble of Laycock ; in the collection 

 of W. Walton, Esq. 



