OKANXA. 



fers greatly from Orbkula, wliich is attaclied by means of a 

 ligament which passes through a fissure in the center of j 

 the lower valve.) There are four muscular impressions l 

 in each valve ; of those in the upper valve, two are near 

 the posterior margin and the other two nearer the cen- 

 ter, but not always very near to each other: of those in ' 

 the lower valve, two are nearly marginal and rather dis- 

 tant, but the other two are nearly central and so close to- 

 gether, that they appear to form but one ; they in general 

 have a small projection between them; and the whole of 

 the muscular impressions in the lower valve, are fre- 

 quently lost by decomposition in the fossil species, so as 

 to appear only three oblique perforations, as Lamarck has 

 described them. The muscular impressions also serve to 

 distinguish Crania from Hi<pponyx^ which has only two. 

 Not one of the three Genera, Orbicula, Crania, and Hip- 

 ponyx, has any hinge ; nor are the valves of any of the 

 Brachiopoda attached to each other by a ligament at the 

 posterior part, as most other bivalves are. The upper 

 valve of Crania has been published as a Patella by several 

 authors : that of C. personata is the Patella distorta of 

 Montagu ; this species having been found on several parts 

 of our coasts, as well as in the Mediterranean. We have 

 represented a fragment of a Pinna, from Cork Harbour, 

 Ireland, upon which are two specimens of 



Fig. 1. C. Personata, Lam. Anomia craniolaris, Linn. An. turbinata,* Poli ; 

 the iriside of the lower valve is shown on one side, and the outside of the upper 

 valve on the other. 



2. Is the inside of the upper valve of the same ; this is the only recent 

 species we know. 



3. Shews the inside of the lower valve of C. Parisiemis, Defr., attached 

 to an Echinus from the Chalk, in Norfolk; we have never seen the upper valve 

 of this species. 



4. Two views of the lower valve of C. Nammulus, Lam. the Nummulus 

 Bratenburgensis of authors ; it is remarkable, that this seenis to have adhered 

 only by a small part of its outside j from Sweden. 



5. Probably the same species, from Meesti-icht. 



6. Shows the two sides of the upper valve of a pretty little species from 

 Orglandes, we have called it CV. costata; its peculiar character may be thus ex- 

 pressed ; Cr. valvula superiore costis prominentibus, radiantibus, octo ad quin- 

 dccem, 



7. Inside of Cr. antirpia, remarkable for the extension of the posterior 

 part of the shell. 



Several fossil species are described by M. Defrance, in 



the lyicfionmiire des Sdences Naturellcs. 



* Poll's figure is referred by Lamarck to Orbicula, 



