124 



This shell forms a most excellent passage between the genus Ano- 

 mla, or rather Placunanomia, and Placuna. It shows the gradual 

 change which takes place between the three genera. In Anomia 

 there are two muscles for the purpose of attaching itself to ma- 

 rine bodies, which form a plug which is free from the sinus of the 

 shell. 



In Placunanomia there is only a single muscle to perform the same 

 office, but in the more typical species of this genus the plug itself is 

 affixed into the surface of the shell, forming, as it were, part of its 

 substance. In Hemiplacuna and Placuna there is no muscle or 

 plug for attachment, and the shells are free ; but in Hemiplacuna 

 there is a rudimentary development of the sinus through which 

 the plug is emitted, and the ligament which connects the shell is 

 of the same form as that found in the genera Anomia and Placuna- 

 nomia. 



Mr. George B. Sowerby kindly showed me this shell, which he 

 purchased with a number of other fossil shells brought from the Red 

 Sea. He informed me that he intends to describe it at length, and 

 give it the name which I have with his permission here used. The 

 specimen now forms part of the British Museum collection. I imme- 

 diately recognized in it the species oi Placuna figured by M. Roziere 

 in his plates of the fossils of the Red Sea, engraved in Napoleon's large 

 work on Egypt. 



The name for the genus is not consistent with the Linnsean canon ; 

 but I use it rather than attempt to form a less objectionable one, and 

 thus burthen the genus with two names. 



Hemiplacuna Rozieri. 



Placuna, sp., Roziere, Description (TEgypte, Min^ralogie, t.l 1 . i.Q. 

 Hemiplacuna Rozieri, G. B. Sow. MSS. 

 Anomia? or Placuna? Desk, in Lamk. Hist. vii. 270, note. 

 Fossil. Shore of the Red Sea; Vallee de I'Egaremeut. 



5. On the Habitat of Cypr^a umbilicata, Sowerby. By 

 Ronald Gunn, Esq. In a letter to J. E. Gray, Esq. 



Mr. Gunn, the enthusiastic and intelligent naturalist in Launces- 

 ton. Van Diemen's Land, from whom we have received so many pro- 

 ductions of that island, has most kindly sent to the British Museum 

 a fine specimen of the above shell, which was described by ]\Ir. Sow- 

 erby in the Appendix to the Tankerville Catalogue. Mr. Gmm in 

 his letter observes : — 



" Cowries, found upon the east shore of Barren Island, one of Hun- 

 ter's islands, N.W. of Van Diemen's Land. Considerable numbers of 

 the dead shell of this species were to be seen lying upon a deep bed 

 of the dead shells of a species of Pectunculus. 



" I will send you a Cowry which is new : it is most closely allied to 

 Cyprcea eximia of Strzelecki, ' Physical Description of New South 

 Wales and Van Diemen's Land;' at all events it is not figured in 

 Reeve's monograph of the genus. It is larger than C. eximia. I am 

 not perfectly clear that it will prove to be the same ; if so, it will 



i 



