390 Mr. Jeffreys on the Testaceous Pneumonobranchous 



lusca ; and, I should think, would not impede the free 

 ingress and egress of the inhabitant. They are noticed 

 by Miiller and Draparnaud, and were considered by the 

 former (to whom both species appear to have been known) 

 as the marks of growth or repair. 



Genus XVI. ANCYLUS. Mull. 



Animal tentaculis brevibus, cylindricis, subtruncatis. Susten- 

 taculum anticfe integrum. 

 Testa conica : apice acuto, recurvo : spird null^. 



1. Fluviatilis. 



Animal grisescens. Sustentaculum postic^ dilatatum. 



Testa ovata depressiuscula, vertice subcentrali, posteriiis 

 inflexo ; fragilis, nigrescenti-fusca, transversim radiato- 

 striata, intiis caerulescens nitida. Apertura subovata. 



Long. 0.125. — Diam. 0.25. 



; Ancylus fluviatilis. Miill. Verm. 2. p. 201. Drap. 



Hist, des Moll. p. 48. t. 2. /. 23, 24. 

 Patella lacustris. Linn. Syst. Nat. 1. p. 1260? Penn. 

 Brit. Zool. 4. p. 143. 



fluviatilis. Da Costa Brit. Conch. 1. t. 2./. 8. 



Gmel. Syst. Nat. 1. p. 3711. Mo7it. Test. Brit, 

 p. 482. 

 «. major, pellucidior, viridescenti-albida ; vertice elatiore. 



On stones in running streams. The variety is found in 

 cold mountain springs, and has often a greenish tinge, pro- 

 bably arising from some minute adherent Conferva or other 

 adventitious matter. 



2. Lacustris. 



