CONCHOLOGY. 101 



cavity large, divided by a horizontal partition, which gives it 

 the form of a half-decked boat. 



Crepidula fornicata. Crepidula unguiformis. 



C. porcellana. C. dilatata. 



C. aculeata. C. Peruviana. 



C. poTxellana. The brown-spotted Crepidula. 

 Shell thick, flat, summit not spiral. 



C. aculeata. The prickly Crepidula. 

 Oval, brown, roughly striated, vertex recurved, interior 

 blue or purple. 



C. suh-spirata. The sub-spiral Crepidula. PI. 32, fig. 2. 

 Species almost round, summit sub-spiral ; colour yellow- 

 ish white, with a bluish tinge towards the summit. 



7. Ancylus. The Lake Limpet. Two species. 



This is a fresh-water shell, found in the lakes of Europe. 

 Shell thin and brittle, obliquely conical ; summit pointed 

 and recurved ; margins simple, base oval and smooth. 

 Ancylus oblongus. Ancylus fluviatilis. 



A. oblongus. The oblong Ancylus. 

 Aperture elongated, vertex turned to one side, striated con- 

 centrically ; exterior pale yellowish colour, interior light blue. 



A. fluviatilis. The river Ancylus. PL 32, fig. 3. 



Simple, oval, almost symmetrical ; summit pointed, com- 

 pressed, very distinct ; bent back a little to the right, but not 

 marginal ; the edges of the aperture entire and effuse. 



FAMILY IV. 



BuLLACEA. Three genera. 



1. Accra. Has no shell. One species. 

 Acera Carnosa. 



2. Bullaea. One species. 

 Formerly classed with the Bulla, but separated from it on 



