Report of the s-iatk Geologist. 515 



the brachial valve, and an anterior expansion which is produced 

 forward into a long cylindrical tube, sometimes attaining twice 

 the length of the shell ; the suture appears on the dorsal side in 

 the median line. Sometimes instead of a single tube there 

 double enrollment resulting in two distinct tubes. The surface 



Figs. 28^-281.— Marginifera typica, Waagen. After Waacjen. 



is ornamented by concentric plications, traversed by line radiat- 

 ing ribs, which are flexuous and close together, the last plication, 

 and the groove accompanying it, is sharper than the others and 



Figs. 282-284.— Productus (Proboscidelld) proboscideus, de Verneuil. After de Koninck. 



marks the separation of the pedicle- valve, properly speaking, 

 from its lateral and anterior expansions upon which the concen- 



167 



