92 CLASS ACEPHALA. 
AcARDA, Brug. OsTRACITA, La Peyr., 
Of which M. de Lamarck makes a family, that he names 
RupistTa. The shells are thick, and of a solid or porous 
tissue. They are now divided into the 
RADIOLITES, Lam., 
In which the valves are striated from the centre to the circum- 
ference : the one is flat, the other thick, nearly conical, and 
fixed. 
SPH ZRULITES, Lameth, 
Where the valves are roughened by irregularly raised plates. 
It is also thought that we may add the 
CALCEOLARIA, 
One valve of which is conical but free, and the other flat, and 
even somewhat concave, so that they remind us of a shoe; 
and even the 
HIPPURITES, 
Where one valve is conical or cylindrical, with two obtuse 
longitudinal ridges on the inside. ‘The base even appears to 
be divided into several chambers, by transverse partitions ; 
the other valve fits like a cover. 
BaTOLITHES, Montf., 334, 
Are cylindrical and straight hippurites. They are frequently 
found greatly elongated. There is much uncertainty, how- 
ever, with respect to all these bodies. 
As to the well known living testaceous acephala, Linnzus 
had united in the genus 
