Dr. 0. A. L. Morch on the Operculum and its Mantle. 117 



1864, and many since made, have convinced me that, so far as 

 regards the British flora, the raphidian diagnosis is not only 

 quite true, but very natural. Yet, as formerly noticed, this 

 character might more easily escape attention in Galiacese than 

 in the other orders. 



Finally, the propriety of retaining Leea under Vitacese has 

 been disputed; and the present observations will tend to support 

 the conclusion of those botanists who, with Adrien de Jussieu 

 and Lindley, persist that this genus ought not to be separated 

 from Vitacese. 



Edenbridge, July 1/, 1865. 



[To be continued.] 



XIII. — On the Operculum and its Mantle (lobus operculigerus, 



pomatochlamys). By Dr. O. A. L. Morch. 

 Ad ANSON* regarded the operculum of univalve shells as an- 

 swering to the second valve of the bivalves — an opinion main- 

 tained by Oken and lately by Dr. Grayt and Prof. MacdonaldJ. 

 In this point of view the lobus operculigerus (Loven), or "the 

 opercular mantle," would correspond with one moiety of the 

 mantle of bivalves. 



Prof. Loven regards the bivalve shell as produced by a cloven 

 or bipartite mantle, and the operculum as homologous with the 

 byssus. 



Prof. Keferstein§ supports Loven's opinion, considering the 

 slit in Emarginula and Tenagodus as a trace of division. The 

 porous slit of Haliotis, Tenagodus, &c., corresponds with the 

 notch or channel in canaliferous shells [Entostomata, Blv.). 

 There is, however, a more important trace of division in many 

 univalves — for instance, the dentated furrow in Monoceros, 

 Pseudoliva, Ayicillaria, and some species of Mwre-r [Cerastes), but 

 chiefly in Carinaria. In this last genus the keel is formed by 

 the two sides of the shell, which are pressed against each other 

 in such manner that a piece of paper can be introduced into 

 the middle of the keel as far as the foetal shell. In Onustus 

 (Humphr.) the two sides are cemented together, but the union 

 can be clearly seen. Akera bullata shows something similar in 



* Hist. Naturelle du Senegal. 



t J. E. Gray " On the Operculum of Gasteropodous MoUusca, and an 

 attempt to prove that it is homologous or identical with the second valve 

 of Conchifera" (Annals and Mag. of Nat. Hist. ser. 2. v. p. 4/6; and 

 Phil. Trans. 1833). 



X " On the Homologies of the so-called univalve shell and its Opercu- 

 lum " (Proc. Linn. Soc. v. 1860). 



§ Bronn u. Keferstein, Die Klassen u, Ordnungen des Thierreichs. 



