139 



Shells longitudinally grooved. 

 Terebratula flavescens Terebratula sanguinea 



dentata caput serpentis 



dorsata truncata 



Terebratula psittacea. 

 [There are also forty seven fossil species.] 



LINGULA. 

 patella unguis. — Linn. 

 Sowerbys Genera, No. I, plate 2. 

 Linnjeus certainly could only have seen one valve of 

 this singular shell, which naturally led him into the 

 error of supposing it an univalve of the genus Patella, 

 particularly as there are no hinge, teeth, or other vi- 

 sible mode by which the valves are connected together; 

 but it has since been discovered that they are united 

 by means of a tubular, fleshy, or membranous pedun- 

 cle surrounding the narrow part of the valves, and af- 

 fixed to marine substances by the base of it, in the 

 manner of the G. Anatifera; the interior of the valves 

 also possess small callosities like those of the Parmo- 

 phora, which have tended probably to confirm the 



