124 , 
This shell forms a most excellent passage between the genus dno- 
mia, 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 hgament 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 of Placuna figured by M. Rozitre 
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 Linnzean canon ; 
but I use it rather than attempt to form a less objectionable one, and 
thus burthen the genus with two names. 
Hemieracuna Roziert. 
Placuna, sp., Roziere, Description d Egypte, Minéralogie, t.11.f.6. 
Hemiplacuna Rozieri, G. B. Sow. MSS. 
Anomia? or Placuna? Desh. in Lamk. Hist. vii. 270, note. 
Fossil. Shore of the Red Sea; Vallée de lEgarement. 
5. On THe Hasirat or CypR#A UMBILICATA, SOWERBY. By 
Ronatp Gunn, Esa. In A LETTER To J. E. Gray, Ese. 
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 Mr. Sow- 
erby in the Appendix to the Tankerville Catalogue. Mr. Gunn 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. 
«J will send you a Cowry which is new: it is most closely allied to 
Cyprea 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. Tam 
not perfectly clear that it will prove to be the same; if so, it will 
