Mr. L. Reeve on the recent Orbiculae. 129 



five specimens, collected by Mr. Strange at Sydney. It comes 

 very near to the West-African species, which has been assigned 

 to C. rostrata of Honinghaus ; but it is of a more convex and 

 roughly solid growth, and the difference of habitat leaves no 

 room for doubt on the subject. The internal posterior scars of 

 the lower valve are obliquely ovate and somewhat isolated, whilst 

 those of the upper valve are narrow and callosely raised. The 

 rostellum is large and prominent. Another character consists in 

 the presence of a delicate tinge of orange-red colour on the outer 

 surface, quite different from the red-stained colouring of the 

 European species. 



The name of Professor Suess being especially entitled to a 

 place in the nomenclature of the Brachiopods, I dedicate this 

 species to him, in testimony of my high sense of the originality 

 and value of his reseai'ches. 



2. Orbicula, Sowerby. 



A genus with the name Orbicula was founded by Lamarck for 

 the reception of a northern Brachiopod, Patella anomala, Miiller, 

 which proved to be Anomia craniolaris pars, Linnaeus, and the 

 type of Retzius's genus Crania. A Mediterranean Crania, 

 Anomia turbinata, Poli, was considered synonymous, but it has 

 just been shown to be distinct. On meeting with the first-dis- 

 covered specimen of the group under consideration, Lamarck 

 created a genus, Discina, for its reception ; while Sowerby con- 

 founded it with the northern Crania, of which Lamarck had 

 made an Orbicula. Sowerby, Broderip, and Deshayes, out of 

 all this confusion, adopted Orbicula for the Brachiopods of 

 which we are treating ; and it appears to me unnecessary to set 

 aside their decision. 



The shell of Orbicula differs from that of Crania in the very 

 important particular of having the under valve thin and horny, 

 furnished with a disk, in which is a slit for the passage of a 

 pedicle of attachment. The disk is subcentral, more or less in- 

 clined to be posterior, and corresponds in position with the 

 vertex of the upper valve. In some species the vertex is poste- 

 rior, and the disk is also posterior ; in others the vertex is a little 

 posterior to central, and the disk is also a little posterior to 

 central. That is the natural symmetrical growth of the shell on 

 a plane surface; but if the animal adheres to a declivitous sur- 

 face, the disk and vertex, which, on a plane surface, would be 

 subcentral, press more posteriorly ; and if the surface be hollow, 

 the under valve is more convex, and the vertex and disk more 

 central. 



Seven species of Orbicula are now known. We have none in 

 the European seas. The original species, found among ballast 



Ann. $ Mag. N. Hist. Ser. 3. Vol. x. 10 



