APPENDIX. 123 



striulae ; umbones tumid, obtuse, considerably nearer the ante- 

 rior side, which forms about a third of the segment of a circle, 

 its slope being convex, and about a third shorter than the pos- 

 terior side ; colour cream-white. Breadth nearly two-twelfths 

 of an inch ; length not quite a twelfth. 



Found among the roots of aquatic plants, in a ditch between 

 Aberdeen and Spital. 



APPENDIX. 



CLASS MOLLUSC A. 



Genus I._NERITINA. 



Neritina fluviatilis, pi. XXIV, f. 16. 



Animal with the sides of the body simple, destitute of elon- 

 gated filaments; tentacles subulate, with the eyes placed on 

 short pedicles at the exterior side of their base. 



Genus II.— PALUDINA. 



Paludina vivipara, pi. XXIV, f. 19, 20, 21. 



Animal with elongated tentacles, and eyes situated at the 

 exterior side of their base ; branchiae always placed in the gill 

 receptacle Eggs of P. impura, f. 35, 40. 



Genus III.— ASSIMINIA. 



AssiMiNiA Grayana, pi. XXIV, f. 17. 

 Animal with very short tentacles, hardly longer than the 

 tubercles on which they are seated, and united to their side. 



Genus IV.— VALVATA. 



Valvata piscinalis, pi. XXIV, f. 18. 



Animal with elongated, tapering, and somewhat obtuse ten- 

 tacles, with the eyes situate on small tubercles at the posterior 

 side of their base ; mouth a little boscidiform ; foot truncated, 



