Lamarck's Genera of Shells. 49 



Shell with two conical, elongated, beak-shaped, unequal valves, 

 disposed at a very open angle, and united at their base ; mar- 

 gin of one valve enveloping that of the other valve. 



Locality unknown. PI. II. Fig. 101. 



Lamarck observes, in addition to what we have already 

 quoted, that the genus Birostrites is certainly very different from 

 his Diceras. Mr. Sowerby having had the opportunity of ex- 

 amining a cast of the inside of a birostrites, is convinced " that 

 it ought to be placed next to diceras, or at least in the same 

 family with chama and diceras, (inasmuch as it accords very 

 nearly with those shells in its internal characters,) and that it 

 should not be placed in his (Lamarck's) family of rudistes." 

 Mr. Sowerby is further of opinion, that " the whole family of 

 rudistes might be struck out ;" for two of the six genera which 

 it contains, sphcerulites and radiolites, he thinks are not shells ; 

 that calceola probably belongs to the next family, brackiopoda ; 

 that discina should be expunged, as being identical with orbicula ; 

 and that " crania is decidedly a brachiopode." We very much 

 incline to Mr. Sowerby's opinion ; but as our professed object is 

 to give the Genera of Lamarck, we do not feel ourselves at 

 liberty to make the alteration he suggests to its full extent : he 

 has, however, so satisfactorily proved the identity of discina and 

 orbicula, that we do not hesitate so far to act on it, as to omit the 

 former altogether. For Mr. Sowerby's arguments we refer our 

 readers to his paper, in the 1 3th vol. of the Transactions of the 

 Linnean Society, 



5. Crania*. 

 « Shell inequivalve, suborbicular ; lower valve almost fiat, per- 

 forated at the interior surface by three unequal oblique holes ; 

 upper valve very convex, having two internal prominent calli. 

 Animal unknown. 



The crania generally adheres by its lower valve, the three 

 holes in which do not seem to perforate it completely, unless 

 by accident, when removed from the body to which it was fixed 

 by the outer surface ; hence they cannot be the issues of mus- 

 cular attachments. 



• Cramum, a skull. 

 Vol. XV. E 



