340 



POPULAR CONCHOLOGY. 



Pentamerus. Sow. (Gypidia Dalman.) — Shell in- 

 equivalve, equilateral ; one valve di- 

 vided by a central septum into two 

 parts ; the other by the septa into 

 three parts; umbones incurved, im- 

 perforate. * — Fossil. 



Dr. Mantell mentions that these 

 fossils differ in their internal struc- 

 ture from all other genera, in being 

 divided internally into five chambers, Pentamerus Aylesfordii. 

 whence the name, which means five 

 celled : several species are known ; P. Knighti Sow., 

 ( Terebratula) conchidium, Icevis, 8fc. 



Family 3.— PRODUCTIVE. 



The mouth arms are fleshy, without any shelly support; 

 the ventral valve has no sort of process, either from the 

 hinge edge or yet from the inner surface, or at the 

 utmost a slight longitudinal support in the middle; the 

 shell is not pierced at the boss, and is either free or fas- 

 tened by means of the upper surface of the ventral valve ; 

 the upper valve is abundantly covered with spines. 



Productus. Sow. — Shell equivalve, equilateral, thick, 

 striated: one valve generally convex, with the margins 

 reflected, and produced; the other valve flat, or slightly 

 convex with the margin reflected ; hinge rectilinear, trans- 

 verse.f — Fossil. 



Strophalosia. King. — Shell with the large valve (oc- 



* Sow. Conch. Manual. 



f Sow. Mineral Conch. 



