390 Mr. Jerrreys 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. Müll. 
Animal tentaculis brevibus, cylindricis, subtruncatis. Susten- 
taculum antice integrum. 
Testa conica: apice acuto, recurvo: spirá nulla. 
1. FLUVIATILIS. 
Animal grisescens. Sustentaculum postice dilatatum. 
Testa ovata depressiuscula, vertice subcentrali, posteriüs 
inflexo; fragilis, nigrescenti-fusca, transversim radiato- 
striata, intàs cerulescens nitida. Apertura subovata. 
Long. 0.125.—Diam. 0.25. 
Ancylus fluviatilis. Müll. Verm. 2. p. 201. Drap. 
Hist. des Moll. p. 48. t. 2. f. 23, 24. 
Patella lacustris. Linn. Syst. Nat. 1. p. 1260? Penn. 
Brit. Zool. 4. p. 143. 
——— fluviatilis. Da Costa Brit. Conch. 1. t. 2. f. 8. 
Gmel. Syst. Nat. 1. p. 3711. Mont. Test. Brit. 
p. 482. VOUS 
a. 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. 
