28 



marked by a suture at the divisions; the operculum in- 

 ternal and bivalve. 



Creusia stromia Creusia spinulosa 



Creusia verruca. 



■ J 



PYRGOMA. 



PYRGOMA CANCELLATA. Leach. 



This genus differs from the preceding with regard to 

 its form. Its valves, being more firmly united, give it 

 the appearance of a subglobular univalve, the interior 

 division longitudinally grooved, the convex back pre- 

 sents an elliptical area, circumscribed by a crenated 

 margin, in the centre of which the aperture is placed; 

 the operculum is bivalve. 



Pyrgoma cancellata. 



ANAT1FA. 



LEPAS ANATIFERA. Linn. 



Mawes Linnceus,fig. 7, plate 2. 

 This should properly be called G. Anatifera; it is un- 

 like all other preceding shells of the Linniean genus 

 Lepas, not adhering by the testaceous base of the shell 



