CHAMACEA. 



729 



is long and straight ; and two cardinal teeth, with a hinder lateral 

 one, appear to be present. 



Family 3. Lunulicardiid^e. — This family is one of very uncertain 

 value, and embraces only the imperfectly understood genus Lunuli- 

 cardium of Munster. In this genus the shell is obliquely oval, 

 equivalve, and inequilateral, the surface being adorned with radiat- 

 ing ribs. The anterior end of the shell is truncated, and the pos- 



Fig. 606.— A, Conocardium giganteum, showing the truncate anterior and produced posterior 

 end of the shell, with the tubular prolongation of the former ; B, Conocardium inflatum, viewed 

 from above : c. The same viewed laterally. Carboniferous. (After M'Coy.) 



terior end is sub-alate. The cardinal line is " marked by a lunate 

 hiatus in each valve, which was probably occupied by the ligament " 

 (Hall). The hinge and muscular markings are unknown. In this 

 genus, as in Conocardium, the truncated end of the shell is some- 

 times regarded as the posterior end. The species of Lunulicardium 

 are found in the Silurian and Devonian rocks, being very abundant 

 in the Silurian rocks of Bohemia. 



Order VIII. Chamacea. 



In this order, represented at the present day by the single genus 

 Chci7na, the mantle is closed, the mantle-cavity communicating with 

 the exterior by apertures for the foot and for the in-going and out- 



