" 
146 Couthouy's Monograph on 
his remarks, Encye. Meth. III. p. 1039, he observes, 
that he is ignorant whether this shell has an ossiculum 
or not, but thinks there are traces of its existence. In 
a number of very perfect specimens examined by me, 
the valves of some of which had never been separated, 
none was found, neither was there the slightest appear- 
ance of any impression on the shell indicative of its ever 
having been present. We may reasonably conclude, 
therefore, that it does not exist in this species. It is 
certainly much to be regretted, that M. Deshayes has 
neglected to mention upon what species of "Thracia he 
observed this appendage. 
pim cta PLICATA. 
Th. testa ovato-oblonga, ihissrersl, ‘wequilaterali, inquo de- 
pressá, transversim plicatà, compress, alba. (Desh.) 
Thracia Ls Desa. Encyc. Mal. Vers, IMI. p. 
1039, No. 
Idem. à Anim. sans Vert. edit. Dish. 1835, 
Idem. Kiener, Iconog., Gen. Turacta, p. 6, tab. 
Description. Shell oval-oblong, transverse, equi- 
lateral, inequivalve, compressed ; beaks small, and 
slightly prominent; valves thin and brittle ; anterior 
extremity rounded, posterior obliquely truncated, and 
bounded on. the outside by a very obtuse angle, extend- 
ing obliquely from the beaks to the junction of the pos- 
terior and basal margins. "The exterior. is strongly 
marked by transverse, rounded, undulating plaits, their 
